I have paddled both for decades.
If you will dive only, and plan to not kayak far to get to your dive site, then the kayak is ideal. If you want to use something for camping as well, the canoe is vastly superior. For the same price and size, a canoe has twice the carrying capacity and can sit two or three people. It is also much more stable. However, as many have pointed out, canoes are not self-draining (as some canoes are) and it is exceptionally difficult to climb into a canoe while you are floating in the water, with or without dive gear, without assistance.