Last year I stayed North in France and then dropped down through Switzerland to Milan, headed for Bologna and turned South for Florence. We got soaked in Switzerland and the police take a VERY dim view of fast bikes and loud pipes.
On the way back we crossed Italy from Florence to Pisa and then crossed the French border staying out of Switzerland all together. This was much better as the roads were much emptier and you stayed South for longer (better weather).
I hate the tunnels, the air stinks and you can't see a blind thing through a black visor. Much better to take a little longer and go over the pass - no lorries, few cars and the scenery is magic.
The A26 / A5 / A6 / A43 basically takes you to Turin. If you get off the peage before the Italian border the route over the top is spectacular and is a closed loop so there is noone on it until you region the other side. The French route takes you through Burgundy so the views are pretty cool and Macon is a good ride from Calais. It has great restaurants, cheap hotels and the best wine in the world all served up in a picturesque little town.
Have fun but don't forget the AA 5 star!