Too strenuous and hot for me, but for the Canal du Midi look upRelaxbiketours.com They cover the length of the Canal between Toulouse and Sete with several pick up and drop off points along the way. Flights to Beziers and Carcassonne are cheap as chips outside the peak period.
I would possibly stick to northern France if thinking of cycling in August, especially if it's been a while. August can be so hot in the South. We take our bikes but mainly use them for shopping/short trips in the summer as it's often too hot to cycle any distance. Around Lac D'orient is fairly flat - http://www.aube-champagne.com/en/cycling-mountain-bike/
You generally find that the major canals such as the Garonne/Midi, Burgundy, Nivere and so on, are bordered by mature plane trees. This makes them far cooler in hot weather.
Trails like the Via Rhona, or the coastal routes do tend to be hot and crowdwd inAugust.
There's a long distance cycle track along the Loire and most of the larger campsites either hire bikes or can suggest companies that do, including e-bikes.
The temperatures are a bit lower than further south and the paths pretty flat, so you might find it a bit tame. But of course the local architecture is pretty striking !
------------- Seeking luxury in unexpected places
Don't forget to leave a review of the French and other European campsites you have visited!
Going to hire a bike and try some 'day trip' cycling when we go to Spain in June and ascertain what we can manage with the heat and choice of normal cycle & ebike.
A few years ago, my daughter and I walked the length of the Canal du Midi. All along the route thee were places to hire cycles, so you won't have a problem. Try the local tourist offices for a list (you can probably get them on line).
When walking, we used a guide book for both the route (not so silly as it sounds as it keeps changing sides of the canal and isn't always obvious)and for the points of interest along it. It also gave some interesting diversions/trips out for cyclists. I got it on Amazon (can't remember the exact title), so a search should find it.
------------- Freedom is a light caravan and an open road.
We have cycled some parts of the Canal du Midi and in summer it's an exhausting business - especially as long stretches are now unshaded with the demise of the huge plane trees.
I too would recommend somewhere further north if you want to do summer cycling - or think about it for a spring holiday instead.