I agree that a 12 guage shotgun is the most versatile, flexible weapon for protection from most everything -including bears. they give you the option of carrying naoise making cracker shells, flares, rubber pellets and light bird shot for less than lethal use and the very best, deep penetrating slugs should deter all but the most determained, largest bruins, and even then I'll bet it could be done.
If we are discussing stopping a wounded bear, that is attacking, then I still recommend a big bore rifle.