I'm a lifelong cyclist, but I have also lived on a boat for a very long time.
My feeling is there are some parts of the canals that aren't designed to be cycled on, and cyclists should accept that. As a cyclist, you are often the fastest vehicle using that space - you should adapt yourself to the environment rather than expect the environment to adapt to you.
I have nothing against anyone riding on canals, but if you get involved with anything involved with towpaths people end up in little self-righteous groups. The boaters hate the walkers, who hate the fishermen, who hate the cyclists, who hate the joggers, who hate the dog walkers. If everyone was just a bit more considerate it would be a much nicer place to be.
If you come to an obstacle like that on the towpath, my feeling is you should not be ashamed to unload your panniers and walk across a couple of times. Or ask a passing boater if they'd give you a lift. I've done that for people in the past.
But generally, if you are on a bike on a towpath you should be prepared to walk sometimes.