If it is a vinyl decal, try heat. Hair dryer or heat gun, warm it up and peel it off. Any glue residue can be removed with mineral spirits of varsol. You could always just face it into the sun for a couple hours and that should be enough heat to soften to glue enough to remove it. If you use a heat gun, be careful since it is a plastic canoe.
The joys of 22 years in the Sign Industry, I know how to apply and remove most vinyl graphics.
Same principal if it is a regular type decal, a little heat always helps, the sun is great for that since we know it won't break the glass. A razor blade works wonders, either just lift an edge and peel slowly and carefully, or, again, slowly scrape it off with the razor. Keep the blade on about a 45 degree angle. Straight edge razor, utility knife blade with the back edge taped for ease of use (you call these box cutters in the USA me thinks).
If it is of the reflective type vinyl it will be a wee bit more tedious. They get the material reflective by adding glass beads to the vinyl compound. Heat works best with this type but it takes longer since it tends to break into smaller pieces. Heat, razor and Patience is key.
Any residual glue again can usually be cleaned with Mineral Spirits or Varsol. Other solvents could be used but the two mentioned should work on a petroleum based adhesive and are more benign than say lacquer thinner and shouldn't affect the vehicle finish if spilled on it.
Any water based or more modern synthesized glue is a crap shoot, but there is always trying to roll it off with a thumb or continued scraping. If you work carefully enough, the glue should come off with the decal and leave no residue.
Actually it'd be safest to keep the sticker and include a copy of the: sales slip, the dealers business license and a photo identification of all parties involved in the transaction. Of course sealed under clear waterproof plastic. If any dog's are involved in the sale or receipt of the canoe, include their license and latest rabies inoculation.