That's where I'm kinda at at the moment too. Just fucking do it or don't already. If you don't want to buy our shit just don't and we will find new markets to sell to. There is an endless queue of people in line to buy Canadian goods, raw resource or manufactured. It's just that the US always made the most geographic and geopolitical sense.
If this is actually an attempt to bring manufacturing jobs back to America (a fruitless and losing battle for most industries but still), then all they had to do was give Canadian industries a heads up "hey, we are gonna slowly wean off of you guys, nothing personal. Hope you find new markets." Simple as. They are not obligated to buy our shit and we aren't obligated to sell it to them either. They're the assholes who pressured us into these free trade agreements and now they're upset that the "invisible hand" of capitalism isn't giving them a handy or has a inherent pro-American bias.
Just a bunch of children that are upset that the rest of the world has finally caught up and/or recovered from the destruction of WW2 and can genuinely compete with the US in just about every regard, especially education and industry. American exceptionalism is only real in the sense that America was the exception to the mass destruction and loss of life in both world wars by being fucking pussies that joined both world wars late and after the enemy was already thoroughly exhausted and bled dry by the Allies. There is nothing particularly remarkable about America in the modern world excluding its vast natural resources and severely over-funded military. They love capitalism but not competition.