Rivendell has many fans, but what their price buys you is a superb traditional road-touring or (smooth) all-terrain frame. I find that their design is less suited to really rough roads such as you'll find in Labrador and especially in the North West Territories. Ditto for Co-Motion, which has a really nice bike, the Americano.

And if you compare prices, Bruce Gordon has a price for the whole bike. You'll end up spending 1000-1200 $ LESS for a Bruce Gordon than for a fully equipped Rivendell. Start with wide tires (700x45 or 26 x 2.25, which can be fitted even with fenders), and replace them with narrower tires around Baie-Comeau. Then switch back to wide tires when you hit the Great North again. And if you go that way, get Bruce Gordon's racks; since they are steel and well crafted, they won't crack with gravel-induced vibrations. To me, the only other suitable racks for the roads you plan to ride on would be Tubus; not much cheaper and not as nice, especially in front.

Other bikes?
I don't know how wide you can go on a Surly LHT (700x35-38 with fenders, I think), but I doubt you can go as wide as you would with a Bruce Gordon. And their cyclocross offerings would work only if you ride with a trailer.

As for the Cannondale Txxx and Trek 520, they aren't flimsy. I have a Trek 520 and it's almost as rigid as a Bruce Gordon. I am sure I would not break it on a tour like yours. That being said, there are a few drawbacks with both of them:
- Too high gearing. On my Trek, I asked the shop to replace the crankset with a mountain one (44-34-22). That was free because I bought the bike during the dead season. Guess what: Bruce Gordon already has such gearing.
- Too narrow tire clearance. I think the Cannondale fits only 700x37. The 520 fits only 700x42 rear and 700x32-33 front. Good for tours in the South, but not in your environment.