If you think about it, you are higher off the water sitting in a canoe than you are wading over your knees. In the canoe you lose some of the solidity of your position when you cast, but you will compensate for that rapidly. Like Ray, I sit in the front seat facing the middle of the canoe to balance it out. My knees would not take the kneeling.

One thing, tho, is that is can be tough to land a big fish in a canoe, if you don't have a net. I learned that steelhead fishing once. Ended up beaching the canoe and landing it from shore, which was almost as much trouble as leaning over and falling out of the canoe would have been.