I think the resistance/drag on water would slow it down a lot and make turning more difficult.
Also, a tippy canoe on ice is no big deal, tippy canoe with a high mounted motor and rudder on water is a recipe for getting wet!
But it is cool to watch!
Imagine it on a Fatboy or some other similar less tippy boat.
I know of a guy who built one out of a 25cc motor. In a pool it pushed an empty canoe easily across. Launching is scheduled for this weekend I believe.
I also recall these being manufactured some time ago under the Dragonfly and Airboy brands. I also recall a video of someone who had an Airboy on the back of a canoe and it pushed him real well upstream. Motor was built like a tank and as heavy as one as well. Sure made a bunch of noise.