Not if you actually want your site indexed by search engines and you want users who do not have the latest browsers to have full functionality. There are also many controls and other HTML 5 elements that are not part of the canvas.
You could reasonably add some small interactions or animations to a page, but I don't see a driving reason to do a whole site using it. There are many other tools out there that are specifically made for quickly creating sites that would work much better.
Just my 2 cents...