President arrives on a state visit, says and does things that offend his hosts and startle even his advisers. That could describe U.S. President Donald Trump in 2017, but it really fit Charles de Gaulle when the French president visited Canada 50 years ago, and shouted "Vive le Québec libre!" from a balcony at Montreal's City Hall.

The visit still strikes sparks in Quebec. A plan by the sovereigntist Société Saint-Jean-Baptiste (SSJB) to commemorate the famous speech on the balcony where it occurred on July 24, 1967, was scotched recently by Mayor Denis Coderre, whose spokesperson insisted that "City Hall is neutral and apolitical." City Hall will, however, mark the occasion with its own week-long de Gaulle exhibition, and provide guided tours of the balcony.

General de Gaulle's apparent expectation that Quebec would become sovereign hasn't panned out, but his rough diplomacy seems to be coming into style. Mr. Trump has offered apparent affronts to the leaders of several friendly nations, including Germany, Mexico and Australia. Former Mexican president Vicente Fox has attacked Mr. Trump's border-control policies in language that no one would call presidential.

Even Gen. de Gaulle's decades-later successor, Emmanuel Macron, went a bit rogue last month after the United States quit the Paris climate-change greement, appealing directly to American climate scientists and entrepreneurs to move to France and help "make the earth great again." High-level diplomacy seems to be turning less diplomatic, and Gen. de Gaulle deserves a precursor's share of the credit.

Some have argued that his balcony utterance was a last-minute slip-up by the then 76-year-old statesman. According to a new French-language book about the visit by Montreal journalist André Duchesne, however, the speech in Montreal was the logical climax of a series of deliberate slights and provocations that began months before Gen. de Gaulle arrived in Quebec City on the French battleship Colbert.

La Traversée du Colbert: de Gaulle au Québec en juillet 1967 digs into private letters, diplomatic notes and memoirs by those close to the events. It paints a sometimes hilarious portrait of an old soldier obsessed with grand gestures, and a behind-scenes marathon of diplomatic mud wrestling over where the visitor would go, and who would receive him when he got there.

"French Canada is bound to become its own state," Gen. de Gaulle wrote privately to an aide in 1963. "This perspective must guide our actions."

France had lost its Algerian colony a year earlier. Gen. de Gaulle had resisted the decline of the French empire after the war, but by the early 1960s he saw promise in a loose alliance of French-speaking states, including Quebec. That suited the newly outward-looking Liberal government of premier Jean Lesage, which established an agency in Paris, and forged new links with a French homeland that had all but ignored Quebec since the fall of New France.

Some federal cabinet ministers grumbled about the "imperialist aims" they saw behind France's newfound interest. They were further alarmed when Mr. Lesage's successor as premier, Union Nationale leader Daniel Johnson, was received in Paris like a head of state in May, 1967. The Belgian ambassador to Canada noted privately that Ottawa was terrified that Gen. de Gaulle's reciprocal Quebec visit would turn into an "apotheosis of bilateral relations" between France and the province.

Gen. de Gaulle was one of many world leaders invited by Canada to celebrate the centennial of Confederation, but Mr. Johnson made a point of saying that Quebec had issued its own "personal" invitation, without asking leave from Ottawa. "We must share the cake," the premier said. Quebec angled for more of the cake by proposing the battleship crossing, which would allow the general to land near Quebec City, skirting the usual rule that heads of state must visit the national capital first.

Ottawa resisted the boat idea, but relented when it realized that the Colbert would have to dock in a federal port. Each side scrambled for a diplomatic prize identified by a front-page headline in The Globe and Mail: "Who shakes his hand first?" Governor-General Roland Michener finally claimed the honour, but the general, dressed in military uniform instead of his usual civilian clothes, more or less ignored Mr. Michener after the greeting.

During an official dinner hosted by the province at the Chateau Frontenac, Gen. de Gaulle saluted Quebec as "a people taking their destiny into their own hands." The Globe's front-page story announced: "Separate Quebec seen by de Gaulle."

The next day, the president climbed into an open Lincoln Continental limousine, for a 270-kilometre motorcade to Montreal along the Chemin du Roy (Highway 138), a remnant of French rule before the Conquest. Fleurs-de-lis were stencilled onto the asphalt, and a replica of the Arc de Triomphe was erected along the route. The Quebec government rented a private radio station so as to provide full coverage, further annoying Ottawa by flouting its control over broadcasting.

The SSJB and local priests had mustered friendly throngs all along the route; the SSJB claimed one million onlookers. Gen. de Gaulle passed through 24 towns and villages, and stopped in six of them. He waded into crowds, and rode through towns standing up, gripping a bar installed in the limo for that purpose. U.S. president John Kennedy had been assassinated in a similar vehicle less than four years earlier, and Gen. de Gaulle himself had narrowly missed being shot during an attack on his car in 1962, yet no one seemed to worry much about his becoming a target in Quebec.

Wherever he stopped, he gave speeches that amped up his rhetoric of Quebec's national destiny. "If this keeps up," Mr. Johnson joked to an aide after a speech at Trois-Rivières, "by the time we get to Montreal, we will be separated!"

The size and enthusiasm of the crowds may have encouraged Gen. de Gaulle to believe that Quebec was hungrier for independence than it actually was. But Mr. Duchesne recounts that the general mulled over the famous slogan during his sea crossing. He asked a senior naval officer: "What would you say if I told them, ' Vive le Québec libre?'" – adding that he might, "depending on the atmosphere."

The famous moment came on the evening of July 24. Mayor Jean Drapeau knew about his guest's previous speeches, and had ordered the balcony to be cleared of a microphone that had been placed there. But it was only unplugged – and easily revived by a technician, when Gen. de Gaulle said he wanted to speak to the people.

Still wearing his military uniform, the general told the large crowd he had a secret for them, which was that his journey across Quebec felt just like his return to Paris after its liberation in 1944. He knew this "secret" would be received in Ottawa like a rifle butt in the guts. "Vive le Québec libre!" was the coup de grâce. It was also the slogan of the separatist Rassemblement pour l'indépendance nationale (RIN).

Federalist condemnation was swift and severe, though it took prime minister Lester Pearson's cabinet nearly a day to muster an official response. Gen. de Gaulle's words were "unacceptable," Mr. Pearson said in a national broadcast. "Canadians do not need to be liberated. Indeed, many thousands of Canadians gave their lives in two world wars in the liberation of France and other European countries. Canada remains united."

Gen. de Gaulle was still expected to visit Ottawa, the PM said, though no one imagined he would, after such a rebuff. The president continued his Montreal visit, touring Expo 67 and the new Metro system. He attended an official dinner at which Mr. Johnson remarked that Quebec and France were linked by " le culte de la liberté." Mr. Drapeau spoke in a different key, saying that France had left Quebec to its own devices long ago, and that "one can't be nostalgic after four centuries."

Sovereigntists, delighted as they initially were, also expressed doubts about the import of the general's sympathy. René Lévesque, who co-founded the Parti Québécois a year later, said that liberation would come through "purely domestic action, or not at all."

Gen. de Gaulle skipped his appointments in Ottawa, as expected, and flew home from Montreal. He was widely criticized in France for embarrassing the country abroad. "I went to Quebec to help the Québécois escape their conditions of subordination," he explained. "I didn't tell them to rebel." He offered no apologies.

Could he have helped in a way that wouldn't have soured relations with Canada, as he certainly did in the short term? Unlike Mr. Trump, who often seems unaware of when and how he breaks the rules, Gen. de Gaulle was a keen student of protocol and diplomatic symbolism. He could easily have found gentler means of showing his support.

In other ways, the general was very much like America's businessman president. Gen. de Gaulle had a grand sense of himself, huge faith in executive power, and distrust for anything that might limit his country's independent lustre. He had no qualms about treating supposed friends abrasively, including, in the early 1960s, the U.S. and Britain. He loved attention, and got it by making dramatic, unexpected gestures.

He was also, like Mr. Trump, sensitive to slights. When Canadian veterans travelled to France in April, 1967, to mark the 50th anniversary of the Battle of Vimy Ridge, Gen. de Gaulle refused to send an honour guard. He was offended that the Canadian government had arranged for Prince Philip to preside over the ceremony. The president was so mad, according to a Globe report at the time, that he nearly cancelled his forthcoming Canadian trip. "It's always the same with these Anglo-Saxons!" he complained.

In the end, he stuck to the plan and boarded the Colbert. He would show them, those Anglo-Saxons in Ottawa. Vive le Québec….

CANADA IN 1967: MORE FROM THE GLOBE AND MAIL