A general answer from me: .357 to .454, with the shortest barrel and largest frame I could get; I'm defending, not hunting. Shoulder holster or chest carry will keep the gun from becoming burdensome. And then because I didn't hear that we were restricted to one gun, I'd also carry a small .22 or .32 for the occasional snake or rabid squirrel. If we are restricted to one gun, I'd still carry the pocket gun and just not talk about it at inspection.
Semiautos? Not for me.
Anyway, your best strategy is avoidance. If you can't tell that a bear is there before you turn a corner and find one 10 feet away, you don't belong in a wilderness service.
Now back to the humdrum reality of my day...