Both canoes and stand up paddleboards (SUPs) are designed to be propelled with paddles that have a blade at one end and a hand grip at the other. The top hand holds the grip while the other pulls the blade through the water with the shaft. Some people use double bladed paddles with canoes and SUPs, but they are in the minority. The construction materials for single bladed paddles are usually similar to those of double bladed ones, but canoeists often prefer them to be made of wood.
Traditional canoe paddles are straight from end to end. They have no discernible front or back and can be used in either direction. Many modern blade designs have a clear power face and a back. There are also canoe paddles with bent shafts. These were once only the domain of marathon paddlers, but they have recently been making their way into every day use. The blade on a bent shaft paddle is angled forward at about 14 degrees to provide more power at the start of the stroke and lift less water at the end.
As with double bladed European paddles, the correct length of a canoe paddle is determined for each paddler and boat combination independently, so that in the normal course of forward paddling the whole of the blade, and none of the shaft, is submerged without reaching or leaning back.
SUP paddles have much longer shafts because the paddler is standing rather than sitting or kneeling. For flat water paddling, the correct length is paddler height plus 10 inches. For paddling in the surf, it is paddler height plus 8 inches. If you plan to SUP in both environments, or people of different heights will use your paddle, it is a good idea to get one with adjustable length.
SUP paddle blades are usually triangular in shape and flat across the bottom. They are angled forward from the shaft in the same way as a bent shaft canoe paddle and for the same reason i.e. more power and less lifting of water. A longer tapered blade is preferable for long distance paddling while a short wide blade is better for riding waves.