Seriously, if a cannon is pointed at you, normally you would think that you should probably step out of the way. To "defeat" this "weapon" just get close enough so that it can't hit you. I mean those things fire like 2-3 rpm. Also a Kung Fu master would most likely make better use of a cannon (hey it fires bigger rounds than a musket), And after you fire a shot you can always whack people with the cannon. But it's a kid's film so what the heck.