The Canal du Midi/ Lateral et Garonne route
is the widest. We took our FP Maldives
(5.3m wide) from Port St Louis du Rhone to Bordeaux and that is the widest boat that can do that if you want fenders as well, and boy you really do need fenders. Height off the water
can be a problem, from memory you are limited to about 3.3m at the center, decreasing at width as nearly all the bridges are arched. No problem with canal width even with passing 3500 tonnes peniche. Canal depth
can be a problem near the canal sides even for a 0.85 m draft
cat so to tie up you often have to come in bows first at an angle and loop a warp round a tree of which there are lots.
Very little fuel
and shops on the canal itself but loads within 0.5 km so a bike is very useful.
The Midi is very beautiful and the whole trip is really enjoyable but you need at least 1 fit person who doesn't mind climbing slimy ladders. The French spend a lot of money
maintaining the system so there are quite a lot of closures out of season and particularly in early spring when they repair banks washed out by floods. These closures are on their website. All in all typically French, you cannot understand how they can afford it but are glad they do