To patch the canvas, you'll want to apply a glued cloth patch. An old bedsheet or similar cloth is your best bet, since it's thin enough not to stick out and get torn off, but thick enough and high enough thread count to form a durable patch and hold the glue. For a hole of this size, a double layer patch would probably be best (one piece between the canvas and the planking, one piece on the outside). Ambroid is the best glue if you can get your hands on some. I know there are other substitutes, but I haven't tried them.
The patched canvas will be very vulnerable to future tears if it isn't backed by wood, so you should try to fit in a piece of scrap planking to replace the broken bit. You will probably need to hold it in with a splint under the ribs. It looks like one of the ribs is broken as well, which you can reinforce by sistering in 8-10" of rib stock, screwed in from the inside.
This sort of repair job will be functional but a little ugly, but it should last until the next time the canoe is recanvassed, at which point you'd want to properly replace the broken plank and rib.