I also agree with the Vallée du Rhône option.
Just keep in mind a second way, west of Paris heading south west of Massif central mountains , in case of strong wings under Lyon that will make you feel the rest of the flight very long with severe turbulences.
Biggest tricky weather areas
Perche: around 100NM west of Paris, south of Normandy region - Very small but sizeable relief that are quickly embedded in every western front
Morvan: Moutains chain around Burgundy: beetween Auxerres and Dijon in the North and joining the Massif Central ( Volcanos chain) in the south. These mount are smaller than massif central, but like Perche quickly blocked in western depressed regime.
Valleys of Rhône (beetween Lyon and Marseille) and Canal du Midi (beetween Toulouse and Beziers) are real venturis, with Mistral and vent d'autan strong and turbulent winds. Theses regimes are oftenly established for several days.
So roughly 2 Options for me:
East : should look like Amiens-Troyes-Dijon-Lyon-Marseille-Cannes-Corsica
West: Rouen-Chartres-Limoges-Toulouse-Beziers-Marseilles-Cannes-Corsica
The second one is longer, but can be usefull in Vs in case of strong southern wind in the Rhône valley. with a C172, it should be taking a long time...
In this season, you can find above the Loire valley the same depressed western weather than in England, so no big issues as the relief can be circled or by-passed. The most delicate situation will be if there is a depression on Golfe de Lyon, in mediterrannea, that generates very active pertubabations wich can block all the South East of France (actually the present situation wich is giving strong inundations in the east center).