It sucks bringing a knife to a gun fight. Know what's worse? Bringing the wrong gun to a bear fight. It's best to learn your options beforehand, rather than relying on vague ideas peddled by other hunters and gun sellers. There are two ideas you must learn how to keep yourself out of the bear's mouth below.

Energy
I’ll say this very clearly. No handgun has the energy to drop a bear in its tracks (barring a perfect, or extremely lucky shot). Even the .500 S&W has little more energy than a .30-30. The handgun is a last resort, slightly better than nothing. Never, EVER rely on a handgun as your primary defense if you know you are going to be in a risky situation. Take a large rifle you are comfortable with, or a shotgun.

Shootability
In my opinion, the issue with packing large-caliber revolvers for bear protection is that they are difficult to draw and shoot quickly — one or two handed. Bear attacks scenarios are highly variable, and can range from giving you a chance to prepare and aim, to being on the ground with a bear on top of you before you realize anything is wrong.

From what I have seen, I would much rather have a handgun that I am very comfortable with, and is very controllable. Recently, I have been carrying either my Ruger .357 Mag or Glock 17 9mm.
I think that with a heavy wheelgun, you will get one shot off if you are lucky. If you’re wondering how you would do, next time you are at the range, see how many hits you can get on a 15” x 20” target at 15 feet in 3 seconds (including drawing from your carry holster). You probably won’t have much more time than that in the field, and possibly less.

While many forum members will brag about carrying a revolver so big that it'll “stop a 900 lb  grizzly in its tracks,” the sad truth to this is that they will carry that huge heavy gun for miles into the wilderness only to be unable to get the sights on target when the beast is “bear”ing down on them.

It's better to carry a gun you're comfortable with and focus your shots on the head, rather than hoping the big bullet digs all the way through the bear's extensive flesh and bone.

For more on this topic, you should take a look and read more at Outdoor Life.