Here is my suggestion which I have done a couple of times and love it.
Assuming you are going in through Calais:
Head to Strasbourg
Enter Germany and get some derestricted Auotbahn down to Basel
Enter Switzerland and head to Luzern on the motorway
Get off the main road and head to Lungern and then Meiringen and head east towards Chur. Some fantastic passes on this stretch
From Chur continue east to Davos then the awesome Fluelapass to Zernez.
Enter Italy on the Umbrailpass (this is the top of Stelvio if you want a quick up and down here)
Through Bormio to Milan then west to Torino
Enter France on the N94 and head accorss to Gap
Pick up the sublime Route Napoleon and head to the coast to Grasse/Cannes
Head east and take in the Col du Turini before dropping down through the tunnel into Monaco.
The head west to Le Mans!
That should make a good starting plan
