We are looking for day river and canal trips that aren't self guided, but I ca only find websites with multi-day cruises. We are interested in other regions as well. We know about the Seine cruises in Paris, but more interested in scenic views of the countryside.
I think there may be day cruises on the Canal du Midi leaving from Homps or Agde. The later is on the Mediterranean end of the canal. If you Google Languedoc-Roussillon you will find a wealth of information about things to see and do in that region, which is my favorite area of France.
Google 'canal cruise Carcassonne' and the same for Beziers and you'll find plenty.
I did one from Carcassonne. It took a couple of hours. I found it by googling Carcassonne canal cruises. It was an enjoyable way to spend part of an afternoon.