I have not found renting a car to be a nightmare in France, unless you want to change your reservation once you have the car, like if you want to extend your rental. Only then did I run into problems because it was a holiday weekend and there were no other cars to rent. But even that was not a nightmare.

You can rent automatics in France, but they are harder to come by. Is there any chance you can learn to drive a manual? You will pay alot more for an automatic, and they might not be readily available. The best solution would be to learn to drive a manual at home to be prepared in case you get stuck with a manual transmission car.

I've been to Bruges, and it's a very walkable city. However, it was nice to get out and see the countryside with a car.

Sounds like a nice trip!