President-elect Donald J. Trump mocked Canada’s prime minister in a post late Monday that described him as “Governor Justin Trudeau of the Great State of Canada.”

The social media post also cited a surprise dinner between the two leaders at Mar-a-Lago over the Thanksgiving weekend and called it “a pleasure.”

“I look forward to seeing the Governor again soon so that we may continue our in depth talks on Tariffs and Trade, the results of which will be truly spectacular for all!” Mr. Trump wrote.

The president-elect has promised to impose tariffs of 25 percent on exports from Canada and Mexico on his first day in office next month unless the two countries do more to stem the arrival of undocumented migrants and drugs into the United States.

If Mr. Trump follows through on his pledge, it would upend the trade agreement among the three countries and be economically ruinous for Canada’s economy, which is heavily dependent on exports, particularly of oil and autos, to the United States.

Mr. Trudeau's office did not immediately respond to requests for comment.

While the two men extensively discussed the effects of tariffs, among other issues during their dinner, there was no indication afterward that Mr. Trudeau had changed Mr. Trump’s mind.

After Mr. Trump announced his tariff threat, Mr. Trudeau took a measured tone, suggesting that the tariff dispute can be resolved amicably.

But more recently, Mr. Trudeau appears to be shifting toward a more assertive posture and on Monday suggested that Canada was prepared to respond with retaliatory tariffs on U.S. imports, echoing a similar stance by President Claudia Sheinbaum of Mexico

Mr. Trudeau noted that Canada pursued a similar strategy during Mr. Trump’s first administration when the United States applied tariffs on Canadian steel and aluminum.

“We will, of course, as we did eight years ago, respond to unfair tariffs in a number of ways, and we’re still looking at the right ways to respond,” Mr. Trudeau told a business audience in Halifax, Nova Scotia.

While Mr. Trudeau called the possible American tariffs “absolutely devastating,” he continued to urge calm.

“One of the most important things for us to do is not to freak out, not to panic,” he said.