For back country you want whatever is the lightest weight gun, .243Win or better, that you can accurately get 2-3 shots from a cold barrel in the vital zone out to whatever range you are willing to shoot.
That, or use whatever you already have, and live with any weight/accuracy/power deficits that entails, since not everyone has the money to go buy a rifle just for back country hunting.
If I get the opportunity to get a new rifle for backcountry hunting it will probably be a Kimber Hunter in .270 or more, unless I find a lighter rifle for less money. If I decide I'm more interested in short overall length, and am willing to trade a little weight for a bigger caliber I might go with a BLR in .358Win.