FWIW I believe pretty much everything is harmonized with the U.S. now anyway.....I think this happened around 2010.
All the B.S. the dealers tell you that you need up here is horse$hit. The American dealer will provide you with everything for free, including the recall letter (which is just a BS statement on letterhead FFS).
I've imported a Subaru WRX, Acura MDX, Porsche Cayenne, and an Audi A4. Nothing had to be changed or altered on any of these cars and the U.S. dealerships were happy to provide me with any and all documentation to get them on the road in Canada.
Piece of cake, tens of thousands saved
If a huge and I mean huge number of people did exactly what you have done then I agree "something" would likely change.
Most likely the manufacturers would throw up more barriers
Subaru covers Warranty but you have to pay and then submit to Subaru US to get compensated. Others would simply refuse Canada warranty coverage which they can and already do. They could simply threaten dealers with sanctions about selling outside their territory which may already be in the franchise agreements.
Even if they didn't throw up barriers the number of cars imported would need to be gigantic for manufacturers to lower Canada pricing scheme and that simply isn't realistic given the need for most people to use dealer financing as well as the travel and inconvenience.
I don't live anywhere near the border. I'd have to buy a plane ticket, get a hotel,take at least 2 days off work and then drive gosh knows how many hours back to NS . Now if I'm saving 20 K on a luxury car it makes sense but for most people that scenario just doesn't work.
I applaud and admire the way you have imported. It just doesn't make sense for enough people to do it to actually have an influence.