Not much hits harder than a 12ga. slug. I think it's a fine choice for bear defense. I would load slug, buckshot, the rest slugs. The only reason I say buckshot for the second shot is b/c although it probably won't kill, it may blind. Your other 4 shots are killing rounds.
"Suppose you were an idiot, and suppose you were a member of Congress, but I repeat myself." Mark Twain