For a longer trip, I might convene in Nice, just because it is reachable by air and semi-central. From there exploring/driving Monaco is close by. After that I’d head to Aix, which is a good base of operations for exploring Arles/Avignon/the Luberon/the Camargue/Marseille/Gorges de Ardeche and Pont de Gard. It is also worth checking out the D559 between Marseille and La Ciotat - it is a great road.

From there, I would head for Turin at whatever pace you chose via the N94 in Briancon. There are an absolutely stupendous number of good roads in the area. You can stay at the Lingotto factory/test track (which is now a hotel) and explore Turin (there is the Fiat Museum and National Automobile Museum) or head to Maranello (3h) or Arese (1.5h) from there. After that, return to Grenoble and then back to Nice via the Route Napoleon.

I’d suggest June since it’s after ski season and before summer tourist season.

Some photos from when we did a similar tour: