I think 10mm or .44 magnum would be best - .45 ACP not so much - a little too slow, probably.
If you mean .45 Colt, as in revolver rounds, you can get them in rounds that are right up there with a .44 magnum, but you can probably only shoot them through a Ruger.
I carry a 10mm Glock 20 in the woods, because of the occasional aggressive feral hog. I have yet to shoot one with it, but I feel pretty good about having 16 rounds of .41 magnum type power available, if I ever need or want it. It is a very accurate pistol that I have regularly hit plate-sized targets with, out past 50 yards. There is a smaller version, the G-29, that is easier to carry, but a little snappier on recoil, or Tanfoglio makes a CZ-75 clone for EAA, in 10mm, that has conventional rifling. That would allow you to shoot 200 grain hardcast lead bullets...pretty decent black bear medicine, I'm guessing.