In calling a halt to trade talks with Canada, President Trump pointed to an ad paid for by the province of Ontario that used a speech President Ronald Reagan made decades ago. In it, Mr. Reagan speaks against tariffs, a tool Mr. Trump has widely deployed, including against Canada, and warns against protectionism.

Mr. Trump claimed that the ad was fake and that it had been aired “to interfere with the decision of the U.S. Supreme Court,” which is considering a legal challenge to many of his tariffs.

The Ronald Reagan Presidential Foundation and Institute said in a statement that the Canadian ad misrepresented Mr. Reagan’s views. The foundation did not immediately respond to a question about how the ad misrepresented those views.

Mr. Reagan’s pro-free trade legacy has become an awkward issue for Republicans, who still lionize the former president as a conservative hero but are now led by the highly protectionist Mr. Trump, who has imposed the most tariffs on U.S. imports since the Great Depression.

In his quest to reorder world trade, Mr. Trump has raised tariffs against allies and adversaries alike, prompting trade clashes and disregarding free trade agreements formerly signed with nations including Canada. According to the Yale Budget Lab, American consumers now face an overall tariff rate of 18 percent, the highest level since 1934.

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