Help fixing a hole in plastic canoe

[RiverRummer]

That eventually happens on every boat like that. If possible, Get new risers and a new seat ( normal style ) and make it last while saving up for a royalex boat. What ever repair you make on this won't be permanent, so don't be disappointed when you have to do it again. I don't think anything works good on these, you'll just be looking for "better" than last time you did this. each time or just get used to doing it more often
to slow up time in between fixes, you might glue a piece on the bottom, and then glue a piece on the top, It's ugly but gives more time between "fixes"
Eventually, you will get tired of fixing it and replace it anyway. when you do call some outfitters at the end of their season and see what they have for sale. I bought one from Byrds on the Mulberry a few years ago, and it cleaned up nicely