a 7mm Rem Mag or 30-06 is a sensible minimum if you're going to tackle Bison & Grizzly bear, although a 338 Win Mag makes more sense
if you are mainly hunting deer and black bear, with the odd moose/elk hunt thrown in, a 270 Winchester, 280 Rem, 7mm Rem Mag, 308 Win, 30-06 Spfd, 300WSM/300 Win Mag is a good choice.
one rifle to do it all? 30-06 would be my pick, in a stainless bolt action with a good 3-9x scope, shooting a premium 180 grain bullet like a Nosler Accubond or Barnes TSX. Shoots plenty flat for peace country whitetail and hits plenty hard for kootenay 6 pt bull elk, and everything in between. Rifles are easy to master with moderate recoil, and ammunition is priced good and easy to find, with alot of options if you dont handload.