I went to the Mashantucket Pequot Museum today, and they had a small exhibit about canoe making; I picked up a couple of tips.
-Make sure the bottom is thicker than the sides
-Build a small fire at the front and rear to harden them.
-Build a fire inside to harden and smooth it out, and put it out when you can feel the heat coming through the side.
Also, build it close to where you're going to use it, because they're really heavy.