In Canada:
Pleasure craft licences are required for vessels used only for recreational purposes, do not carry passengers and are powered by an engine of 10 horsepower or more unless they are registered in the Canadian Register of Vessels. There are no fees to license your pleasure craft. It is good for ten years.
So you don't need to for a 9.9 powered dinghy, but hey if you do, it's free!
Note: Licensed in Canada = Registered in USA. Registered in Canada = Documented in USA