Well, I don't see why you shouldn't join the Air Cadets.  A lot of our fighter pilots were in the Civil Air Patrrol over here as kids, and a lot of CAP cadets go to the USAFA. 

About joining the Canadian military...you could probably get a fighter slot.  I know that it seems difficult, but, hey, obviously people do make it.  If nobody tried there wouldn't be any pilots.  As for our service academies, they do take international students.  You are not commissioned into our military, but it would probably look good if you went back to Canada and you tried to get a pilot slot.  Here is something that might help you.  It is for the USAFA, and it is probably the same policy for the other service academies, too.

http://www.academyadmissions.com/admissions/howtoapply/international.php

Good luck!