If Donald Trump gets elected, the wall might be built, but it will be the Canadians building that wall. Lots of Americans say, "if Trump or Cruz becomes president we will move to Canada." Well, Canada could be easily overwhelmed by immigrants. Immigrants from USA. They might want to build a wall, or at least more strictly enforce immigration laws. They are pretty strict about enforcing immigration laws now.
It's actually not easy to immigrate to Canada. Kind of like officially immigrating to USA; the number of legal slots is limited.
With 320 million Americans and only around 50 million Canadians, I can see them looking at the numbers and saying, "can we absorb the flood?"
Someone from Canada responded to one of my comments saying Canadians might welcome refugees from USA under Trump, but look askance at refugees from a USA under Bernie Sanders. Those refugees would be right wingers.
Folks will say, don't worry, Canada has lots of room. It has the second biggest land area in the world, but much of it's space is in the harsh north. Also, northern Canada is land of the Inuit peoples who's lifestyles require lots of space. These native folks often rely on hunting and fishing so they don't want to be hemmed in by a bunch of fleeing Americans. Remember, the Inuit, Native American and Eskimo people were here first.