This largely comes down to anti-competitive practices and relative economic output. Canada has a far weaker economy than the US - we've honestly just got a lot

This largely comes down to anti-competitive practices and relative economic output. Canada has a far weaker economy than the US - we've honestly just got a lot fewer people up here - and the US can leverage it's geopolitical power to force other countries to abide by it's laws. If we don't blink when an unequal trade treaty opens up natural resources to private american exploitation we probably shouldn't blink when a country establishes a law that favors it's domestic product over imported. And actually, I believe the US does dump a significant amount of money into both enforcing the "Made in America" mark on products and advertising to buy American - that too is trying to tip the balance toward consumption of a domestic product. And, lastly, unlike in America, in Canada the free market is not held as the solution to all problems - going out of your way to support and help fellow Canadians is a virtue that's widely celebrated.