Canal boats are lovely but can be hard work with only two adults. He'll be crawling around that age, won't he (memories are all very vague, sorry). Do you think you can keep an eye on him at all times while one of you is steering and one working the locks? Locks involve jumping off the boat - how is the steerer going to make sure ds is safe while controlling the boat?
I like canal holidays but think about it carefully, check the route out (make sure you there aren't locks every mile or any flights of locks) and aim to go not very far at all!