A Glock 20 (10mm) is the go-to pistol for bear defense in Alaska today.
They say they like the Glock 20 because of the number of rounds it holds. But, have you ever seen a grizzly run? You're not going to get more than two or three shots off at the most. And, unless you're experienced, you will likely miss the first shot because of the way they charge you with their head down. I think I'll stick to the 44 rem mag revolver for a grizzly sidearm.