Keep in mind that the more specific to a particular use a boat design becomes, the less capable it will be for other uses. On the other hand, the canoe that will serve you for canoe tripping or a family outing could be outfitted and pressed into service for whitewater use, but you'll be limited to low water and low-gradient rivers, with less complicated rapids. Painters' knee pads would provide some purchase on a slippery hull, but the more enterprising and committed river runners would glue semi-permanent knee pads or cups to the floors of their canoes. If you were truly in the avant-garde, you would have found a way to attach D rings to the floor and sides of your canoe, to provide attachment points for thigh straps. Some old-timers even managed to Eskimo roll their Grumman aluminum canoes.
Control is the objective.
Your success in running a rapid is partially measured by how dry you can keep the boat. A good line, carefully executed strokes, and judicious timing and adjustment of boat leans can bring a canoe through a tough Class IV drop, completely dry. But these skills take time to develop. As water levels increase, your ability to run a dry boat correspondingly decreases. So one thing you'll need is lots of supplemental flotation, that is, in addition to the hull itself, which will have at least sufficient buoyancy to keep it from sinking when swamped.