Bear attacks end up being close quarters more than people think which would give a slight edge to the hand gun although I still think a good ole 12 gauge with slugs would be pretty good otherwise.

One example of close quarters attack is from a patient that was treated for a puncture wound in the office I work at. The guy was out hunting and had a rifle over his shoulder and a .44 mag on his hip. He heard a rustle behind him and turned and saw a grizzly bearing (pun intended) down on him closing fast at about 10 feet away. He barely had time to throw his left forearm up in its mouth and was knocked in his back with it on top. He was able to reach for his .44 and unloaded all 5/6 rounds into its gut at point blank range. The bear finally got off after the last shot and slowly walked away. He said it stopped and looked back at him at one point and he thought it was going to come back and he was terrified because he was out of shots with his .44 and couldn't use his other hand to get his rifle up to shoot but it turned back around and continued away.

Anyway, point is, rifle or shotgun wouldn't have done this guy any good and that might be what would give a big caliber handgun an edge, plus the semi auto like you said.