I've not travelling to France with my dog and the MOG but do often take him with me in the car. For me at least, I would think twice about it as it's super easy for him/her to want to jump out and even with a harness and tether, my little guy gets too excited with all going on around him.
More importantly, I have to plan when I take him around cooler days. With no AC and generally the cabin heating up slightly due to the design of the car, I found out quickly he got quite overheated quickly.
Perhaps put a cooling matt in the footwell if your dog fits there,
Good luck!
