Here's a slimmed down version of the map to give an indication of the potential for a French map.
Imagine starting the game in the south-west, at Gap. You travel down the mountains to Nice, and follow the coast towards Marseille. You then go up through the mountain pass to Lyon, and there's a desert in the yellow area between Dijon and Metz. (assume you have to go straight and can't go from Dijon to Tours).
After Metz, you get to Paris. There's a variety of options you could take then. I imagine Brest to be a big port city. You eventually get to Bordeaux. There's forestry in the Bordeaux/Bayonne/Toulouse triangle, so perhaps put a large forest there. You have the final Gym in Toulouse, and climb Victory Road to the Pokemon League near Super-Besse.
Of course, this all works in reverse too, maybe better! Start at Super-Besse, reach Toulouse, cross a forest, get to Bayonne...etc. Culminating in a beachside final Gym battle in Nice, and the Pokemon League at Gap.
It's just an idea, but it makes France a very exciting place for a game all on its own.