Even before APTA, most Of the Big 3’s offerings were available in Canada, but anything that wasn’t produced there was at a substantial premium to the domestic stuff. Lincolns, Cadillacs, Imperials, Oldsmobiles, Buicks, Mercury Monterreys, Edsels etc. could be had.
The Big 3 produced powertrains in Canada, but in much narrower ranges. Essentially inline 6 and small block V8s, 3-speed manual transmissions, and the lower capacity automatics, and a limited range of drive axles. Body stampings, wiring harnesses, and other systems were sourced locally, again without the flexibility that U.S. customers enjoyed.
Owing to preferential British Commonwealth tariffs, all three exported to the Caribbean, Africa, and Australia, as well, being the respective parent’s primary product source.