I just remembered something. Back at the end of the 90's and early 2000's there was a great influx of Chinese students into Canada, as well as the U.S., but if I remember right, Canada was getting a large chunk of them, and I remember wondering why. Seems relevant somehow.
Not to mention all the draft dodgers that went into Canada during the Vietnam war. If you can't attack America directly, how could you? You need a way to get ground forces on the continent. Think about it.
Something else to consider. America has a very heavily armed citizenry, and we know how to use it. So, I would suspect that our enemies would seek to destroy our morale and will to fight back. How could you do that? Lies? Propaganda? Where would that come from? Who is complicit?