Re: Hand Gun
Availability, weight, and configuration, are more important than actual caliber to me. If it's too heavy you won't bring it, if it's not configured in such a way you can put hands on it right now (not stowed in a pack) it won't be available. If it ain't available when needed it's not much good.
Bears come in a lot of sizes, and can take a wallop, and keep moving. Wound channels long enough, and wide enough to disrupt vital organs is the goal. Having something is better than nothing, but finishing the job may save someone else problems down the road.
I think minimum is the .357 magnum in something like Buffalo Bore hard cast 180 grain bullets. My Ruger Blackhawk .44 special with the Buffalo Borehard cast 255 grain bullets is a favorite. The Smith & Wesson Scandium might be the optimum balance between weight and power allowing you to step up to 300 grain FMJ's like Barnes.
There are bigger more powerful handguns out there, but bears are notorious for having little respect for ft lbs energy, but if you're in brown bear country they also offer a bit more penetration with heavy properly constructed bullets.
Packed in something like the Alaska Guide Holster will have it available more often than not.