Most pepper spray should suffice against bears. Whistles are a good idea, as well as a noise maker like little bells on your person.
The key is to know how to identify bear scat to see if you are in the territory of a dangerous bear. If you see seeds in the scat, and it has a berry odor, then you are probably in black bear country, and the risk of attack is small. If you are in Grizzly bear, or "dangerous" bear habitat, most of the bear scat will have little bells and whistlesin it and smell like pepper
Another good thing to do if you are in dangerous bear country (where you can carry a side arm) is to file the front site offyour pistol. That way it doesn't hurt as much when the bear sticks it where the sun don't shine