A ways back, there was a push to include the origin in the posting, but it never really took. There really aren't that many offers of stuff from Canada, the UK or elsewhere to make it worthwhile. It would be reasonable for people who are posting stuff outside of the US to include the country of origin, but I'm willing to bet that doesn't take either.
As far as shipping to Canada goes, it isn't that much worse that shipping within the US, so long as you don't use UPS (I've also had trouble with Fedex Ground) or aren't trying to ship at magazine media rate. Having said that, a wise man once said, "anybody in the coin-op hobby in Canada should definitely get a US address".
If you are looking for coin-op stuff for sale in Canada, I would also check the CGCC and MAACA forums from time to time.