I'd go up the Med coast to Girona

You could consider a night each in Bilbao, Bordeaux and Blois - the three Bs! The drives aren't too long between destinations so you would time to do a bit of sight-seeing.

When travelling to some cities you should beware of low emission zones.
France has one and system an that is not compatible with the Spanish system.
I would expect the French car to be newer and have the correct stickers.
However, entering Spain it will not. And there lies the issue with your plan.I will leave you to do your own research because there are way too many cities and towns with such arrangements, then variables like no foreign vehicle regeistration, times and areas etc.

San Sebastian is a good place to stop just before arriving in France. Bordeaux would be a good next stop, although you know that the weather will not be ideal, probably. From Bordeaux, it's a straight shot back to Paris.

VANAARLE has a point about emission zones.