Im not sure if it'll let me post a link but look up RickShaw mud motors (
https://vimeo.com/1319804) its nothing fancy basically just a weed eater with a prop but for that small of a boat and if you don't care about speed it might be a good option, also Stump jumper makes a light 7hp mud motor (63 lbs) but that might be a bit much for the back a canoe unless you can find a way to reinforce it