Okay, but I'm not sure I see the connection between Trump not building the wall yet, and Canadians and Mexicans switching geographic locations. In fact, if that were to happen, but the countries' economic situations stayed the same, Trump would probably still build the southern wall, to keep the now impoverished Canadians out. And Mexico might build their own southern wall again, just like they did in Mexico, only this time to keep Americans out.
Walls are a time-honored tradition when it comes to protecting borders. Trump just took lessons from the Chinese and Mexicans.