It seems we are all talking about a strictly defensive situaltion here and not hunting.
That makes a big difference in your tactical approach to the type of weapon you choose for protection.
This would be a last ditch s.h.t.f. "I'm about to become dinner" problem.
That said your only hope of avoiding getting the big chomp would be to stop the animals aggressive behavior instantly, or as near instantly as possible.
The only way to do that is to interrupt the central nervous system or cause an instant drop in blood pressure.
Since ranges would be quite short your time element window is extremely small.
That pretty much rules out shooting the bruin in the gut, chest, foot or other area that won't STOP the thing. Casuing a massive drop in blood pressure with any handgun is very, very unlikely if you are being threatened nose to nose.
You probably want to brain the beast.
That said a .357 magnum with good bullet would work as well as any of the big bore busters.
No, boys and girls I am not advocating the .357 over the other choices.
I am advocating something you will want to pack all day.
If the size and weight of the arm is too much you might decide not to take it the very day you would need it most.
Personally I'd opt for a 12 gauge with the correct slugs but I do understand that carrying a 12 bore while back packing or fishing could be problematic.
I have two Rugers, both .45 Colt calibers. A Vaquero 5.5" and a Bisley BH 7.5".
The Bisley with max loads under a 300 grain flat nose harcast would get my attention.
I also have a M-29 and four or five .357s but for defense against the bigger than me bruins the Bisley BH in .45 Colt gets the nod.
The prblem with an attacking bear is hitting the thing in the brain.
(or the spine)
If you cannot shoot the big bores with heavy loads accurately, and quickly, then the maybe a well placed shot with the more controlable .357 would be better than missing the brain with a cannon?
Tactically there is a huge difference between hunting and defending yourself.
When hunting you have time ans distance on your side.
In a defensive situation your time is short and the distance short and getting shorter.