When I canoe and kayak train it is always 2 hour duration. I think you are right Lauren about blockages/hernias from sit ups, crunches etc. If I get this resolved with surgery or more time, I QUIT with regards ab exercises.
Yeah 2 hour durations are definitely quite extensive, especially since its similar to weightlifting- as we know already, weightlifting can cause a lot of abdominal problems. I think you definitely need to fall back on that for sure. I would try to keep it between 30-60minutes if you truly cannot go without canoeing/kayaking.
And yeah definitely, I would definitely recommend not to do those abdominal exercises since you are having problems and considering your age. A lot of gastros/people do not know about abdominal exercises causing all of those problems, I learned about all of that stuff recently from other J-pouchers and on the internet.
Definitely do less extensive stuff. Also overeating can cause blockages, hernias, and other stuff too. So definitely be careful with not overeating as well.