A spritsail is about the easiest to operate and most user-friendly rig that can be put on a small boat or canoe. If equipped with a brailing line (which when pulled, quickly squishes the sail and sprit up against the mast in a bundle) it's also the fastest to furl and/or deploy. The biggest drawback to them tends to be limited downwind performance with the sail hanging out to the side. The lower corner tends to curl inward, toward the hull because they have no boom, and you temporarily lose valuable wind-catching sail area. The addition of a simple sprit-boom the package will help support the bottom corner when sailing off the wind, but will prevent being able to brail the sail (unless you detatch the boom from the clew corner first - as you will learn, canoe sailing is all about compromises, it's just a matter of which ones you want to make.)
Gaff sails, on the other hand, tend to be about as complex, technically intricate, unforgiving to rig and non-user-friendly as anything you can hang up there. Yes, they can certainly be used on a canoe and can work fine, but most of the people who use them do so because they enjoy playing with a lot of rigging. Canoe-sized gaff sails tend to be rather stiff due to the weights of available fabric. Getting one to set nicely can be quite tricky since the various halyards, lacing and fittings are all pulling on the cloth in different directions. They have a nice "salty" look which some folks desire, but the general opinion is that they're usually unnecessarilly complex. A better option in a four-sided sail might be something like a lugsail (either balanced lug or standing lug) which can have a very similar profile and look, but with more simple rigging.
Left to right: Spritsail, Standing Lugsail, Chinese, Junk-style balanced lugsails, Tanbark (brown) balanced lugsails with striped spritsail and lateen-batwing hybrid. I don't seem to have a good photo of a gaff canoe sail handy since not many people order them. You can just barely see the brail line and brailing eyelet on the striped spritsail. It leads from the deck up to the masthead and out around the sail and sprit, surrounding the sail, and back to the mast. When you pull the line on deck it gathers the sail up against the mast. The weight of the line hanging there tends to put a small "dent" in the leech edge, but not enough to really harm performance. Pulling the line and brailing the sail against the mast (or letting it go to unfurl the sail) only takes a couple of seconds, so it can be a handy thing for launching, landing, etc.