For months, U.S. President Donald Trump has griped about the U.S. trade deficit with Canada. Never mind that the shortfall is entirely a function of his country buying so much cheap, reliable Canadian oil. The Trump administration’s obsession with tallying up the cross-border flow of goods completely misses one of America’s biggest trade wins: the billions of dollars of investment by Canadian parts makers south of the border, and the huge number of jobs that have come with it.

At least 25 Canadian-owned auto parts companies operate more than 170 plants across the U.S., according to an analysis of corporate filings and company websites in consultation with the Automotive Parts Manufacturers Association, a lobby group that represents the Canadian industry. The APMA maintains an inventory of both member and non-member auto parts companies with plants in the U.S.

It’s a significant manufacturing footprint, stretching across 26 U.S. states, though heavily concentrated in Michigan. Magna International has the largest reach, with 55 U.S. plants, followed by Samuel, Son & Co., Woodbridge Group, Linamar and Martinrea International.

It’s hard to say how many investment dollars those plants represent, but when land, equipment and start-up costs are factored in, the new plants easily cost between $50-million and $250-million each, according to Flavio Volpe, president of the APMA.

“We’re talking about tens of billions of dollars that Canadian companies have made in the U.S.,” he said. “Everyone is focused on imports but they’re ignoring the fact these Canadian companies are big American employers.”

The APMA estimates nearly 48,000 workers are employed at Canadian-owned parts plants in the U.S.

On March 4, Mr. Trump unleashed the first of his promised tariffs that threaten to upend the auto industry with 25-per-cent across-the-board tariffs on most imports from Canada. Those are set to be followed by 25-per-cent tariffs on steel and aluminum as well as reciprocal and automotive tariffs that have yet to be defined.

In early February, Linda Hasenfratz, the executive chair of Linamar, warned that within a week of tariffs being put in place “we would see vehicle production in North America grind to a halt, and that means millions of people laid off, the majority of which would be in the U.S., and I can’t see how that’s a good thing for America.”

If shutdowns do hit Canadian-owned plants in the U.S., the pain could disproportionately fall on Republican-held regions. Of the 173 plants tracked by APMA, more than 70 per cent are located in congressional districts controlled by Republicans, according to the association.