Carry whichever one of the 3 you feel most comfortable with and pack a good sidearm in 45 Colt.
In sheep country, a sidearm's gonna get real heavy real quick. It's kinda pointless to save a half-pound of rifle weight then strap on 2-3 lbs of handgun.
If 'twere me, I'd take the .300 if by myself--it may or may not make a difference on a grizzly, but I'd feel better with a bigger gun. .270 if guided or with a partner.
