All else being equal, a shorter barrel is going to be stiffer than a longer barrel, and intrinsically more accurate. However, with a shorter barrel powder charges are less likely to be fully consumed, meaning faster powders will be better, and velocities will be lower, or perhaps less consistent.
I would think that beyond a minimum length, the shot pattern for a short barreled gun would be about the same as that for a long barreled gun (same terminal choke).
But, first things first. If you're hankering for a canoe gun, do you already have a canoe?