There's flotation in each of our pleasure hulls to keep it afloat if filled with water. Royalex® canoes have foam cores giving flotation. Most composite hulls have sealed-air tanks. Tuf-weave® tandems with a Flex-core have polyurethane-filled end tanks.
However, even though our hulls float filled with water, we strongly advise supplemental air flotation bags for Class II rapids or above. If swamped in rapids, a hull must not just float, but float high to avoid hidden rocks.