I'd speculate that you'd be dealing with the equivalent of a big brown bear, so a .308 or 30-06 as minimum rifle caliber up to 300 magnum, 338 magnum, or 375 magnum maximum, or a 12 slug gun at ranges up to 100 yards. Handguns should be 357 magnum minimum, and any handgun bullet should be solid for maximum penetration.
I like large capacity magazines, even on my hunting rifle. The larger the magazine is the greater opportunity to put lead in the subject before it gets into cover.