Mountain bike rider/racer here. Your best bet is still Kijiji or Craigslist, and most of the good stuff is probably closer to the city. I haven't seen much locally listed on there and I check 2 or 3 times a week.
There is a classifieds section here, but I don't think you will find too many bikes posted, at least that are suitable for racing and not from a department store.
Pinkbike.com classifieds are also a good place to check out, and there are quite a few Canadians on there.
http://www.pinkbike.com/buysell/You can also check out the Canadian Cyclist classifieds:
http://www.canadiancyclist.com/classifieds.php