2 3/4" slugs, any style your gun shoots well should work. For buckshot, I'd probably go with 3", 000. In my experience with deer, those things break bones like matchsticks. You'll have to check your gun of course, but my old 3", 1100 would put the entire charge of 000 into a circle you could cover with a coffee cup at ten yards. (I discovered this when a little tree jumped between me and a deer once.) I suspect they'd be pretty bad bear medicine.
For God so loved the world, that He gave His only begotten Son, that whoever believes in Him should not perish, but have everlasting life.
John 3:16 (NKJV)