Black bears and polar bears appear to be less aggressive than grizzly bears.
I read once though that if you spray a black bear with pepper spray, it will deter them for a short while, but that they might come back more aggressively. I dunno if that is the case, and don’t want to test it lol.
Depending on the shot size I think you could get vastly different results. #4 would definitely do damage at close range, but a pheasant or dove load unless shot directly in the bears face probably would sting a bit. I’ve shot 8 1/2 at a plastic milk jug at 20-30’ and had it not come out the back side.