[Redliner]

Don't buy a bike from Wal-Mart or Canadian Tire if you can avoid it. Bikes from big-box stores are made with crappy components and put together by teenage kids working for minimum wage who have a marginal understanding of what they are doing. If you intend to actually ride the bike, you'll probably have trouble with something like the CCM.

You will get more for your money buying from a local bike store, although you might have a tough time getting under the $400 mark. It's not impossible though - try looking for last-years models on clearance. The Bike Shop has the 2013 Specialized Hardrock for $399 right now - they're out of your size but there may be other deals like that out there. If the Trek 3500 is too expensive but you like the brand, look at the Trek 820. Should be right in the $400 range. You'll probably be giving up the disc brakes, but for the riding you're planning on doing V-brakes should be fine. The nice thing about buying from an LBS is they'll usually include some kind of service package with the bike. Calgary Cycle & Pure Cycle include lifetime free tune-ups. No limit - as many as you need, for as long as you own the bike. Try getting that from Wal-Mart or Canadian Tire.

If the LBS route isn't going to work, even Sport Chek has some decent bikes these days. They sell GT and Jamis now and I think they had a decent GT for right around 400 bucks as well. Good luck!