I'm on the Rock too. For big game, my starting point is the 6.5X55mm Swede. The .243 Win can take big game cleanly, but there are better choices out there.
Why limit yourself to those cartridge choices? The .270 Win, .308 Win, .30-06 SPRG are all fine Caribou and Moose cartridges and you can find them in any local Canadian Tire, Wal-Mart or hardware store that still sells ammo. 130gr bullets in the .270, or 150gr in the .30s make for great Caribou rounds. When you switch to Moose, you can bump up to 140gr or 160gr in the .270 & 180gr in the .30s.
If you opt for any of the more esoteric calibers, I strongly urge you to start reloading, as factory ammo is going to be a real biatch to find locally. Those extra shipping and hazmat fees really start to add up every time you need more ammo!