Trump tariffs threaten Detroit’s cross-border auto legacy

The tariff fight is hitting a supply chain that was built to cross the border, not stop at it. In Detroit, Ontario and the cluster of parts plants that bind them together, any pullback by U.S. automakers in Canada would echo through jobs, machining lines and assembly floors on both sides of the border, where decades of integration turned auto production into a shared North American system.

That system began with the Canada-United States Automotive Products Agreement, signed in 1965 and better known as the Auto Pact. It linked the Canadian and U.S. auto industries into one market, after Canada in 1964 faced about a $600-million trade deficit with the United States and Canadian vehicles were roughly 50 per cent more expensive than U.S. vehicles. The agreement helped turn automaking into one of Ontario’s major industries. It was later found to conflict with international trade rules and was cancelled in 2001, but its deeper legacy was the integrated manufacturing web that still ties Detroit to Canadian plants and suppliers.

Donald Trump’s trade war now threatens that web. The United States imposed 25 per cent tariffs on Canadian automobiles on April 3, 2025, after already levying 25 per cent tariffs on Canadian steel and aluminum on March 12. Canada retaliated with 25 per cent tariffs on non-CUSMA-compliant fully assembled vehicles imported from the United States and on the non-Canadian and non-Mexican content of CUSMA-compliant vehicles coming from the U.S., effective 12:01 a.m. EDT on April 9. Ottawa also created a remission framework for auto producers meant to encourage production and investment in Canada and protect Canadian jobs.

The political pressure is sharpened by the scale of the industry. The Canadian government says the U.S. tariffs directly target an auto sector that supports more than 500,000 Canadians. Unifor, the country’s largest private-sector union, warned in August 2025 that the industry was in the “fight of our lives.” The union said the tariffs threaten tens of thousands of jobs and billions in manufacturing investment, and that disruptions to the integrated North American supply chain could trigger production stoppages within days.

The economic costs could spread well beyond border cities. TD Economics said in May 2025 that if the tariffs remained in place for a full year, U.S. auto sales could fall 4.0 per cent and Canadian sales 7.5 per cent in 2025, warning of a protracted decoupling of North America’s auto industry. Canada has already shown it is willing to use tariff relief and import quotas as leverage, later limiting tariff-free vehicle imports for General Motors and Stellantis after production shifted away from Canada. That leaves Detroit’s cross-border legacy exposed to the politics of trade war, with the cost measured in investment, output and the industrial ties that made the region work.