Personally, I wouldn't want a charging bear to get close enough to me to where bear spray might be effective.

I would prefer, in this order, a powerful rifle, a powerful handgun, and a can of bear spray. My choice is dictated by how close the bear has to be to you for your chosen protection method to have half a chance of being effective. At ten feet, bear spray might well be as effective as a handgun. But I don't want a charging bear to be ten feet away from me to find out!

A rifle could take out a bear (assuming appropriate caliber choice and marksmanship skills) from 100 or 200 hundred yards away. A handgun would probably be limited to 25 yards (assuming you choose an insane caliber). A can of bear spray would be limited to only a few feet or yards. Now, how close do you want that charging bear to get to you? Personally, I'd want all three options. And if possible, I'd throw a hand grenade into the mix as well, as an additional choice.

Better yet, try to keep yourself out of "charging bear" situations in the first place. None of your options are really that great once the brute is coming at you.