Many of our members are attending our yearly Assembly, so hang on for a bit... someone who knows more that I do will jump in eventually.
In measuring a canoe, imagine putting a plank against the bow and another against the stern, so that they are vertically level, and measure from plank-to-plank. This will give you the canoe's length. You are measuring the farthest outside-point at the bow to the farthest outside-point at the stern-- but measuring straight, point-to-point, without measuring the curve of the canoe. It may be a few inches off, either way-- i.e. a 12 foot canoe may actually measure 12 feet 4 inches or 11 feet 11 1/2 inches... but the company that made it called it a twelve footer.
Pictures help a lot... a shot of the deck, the profile, and the interior-- showing seats/thwarts/ribs, would be nice.