You would have to point it out to me if I'm wrong but I don't think anyone in this thread has said Canadians would cross the border to catch a flight to go back to Canadian cities.
You did mention it a few times but I don't see where anyone ever disputed you about flying back to Canada, they just argue that some Canadians will cross the border to catch flights to destinations in the US or other countries.
Crossborder choices can impact an airport for certain types of flights. SAN is a busy airport in a metro area of 3 million with many international ties, but it has only a couple of Mexico bound flights. Why? Residents choose to cross the border into Mexico and then take flights out of TIJ.