Leaving from Marseille there are numerous things to see on your way to Paris. If you plan to spend any time in Marseille, there are many Greek and Roman ruins within the town, as well as Notre Dame de la Garde church, still marked by bullet holes from WW II. The calanques outside of town are a relaxing way to visit the Mediterranean coast. Heading out of town, Les Beaux is a must-see...continuously occupied for what seems to be forever. St. Remy de Provence, Arles, Avignon...all of the towns of Provence have their own flavor. The light seems different in Provence; it sparkles. Visit the smaller towns in Provence and the Luberon. Try the Cotes de Rhone wines, smell the lavender, taste the rich variety of fruits and vegetables that flourish here. Be laid back.
If you are not spending time in Paris, take some time heading there to visit Beaune and Bourges in Bourgogne. The Hospice de Beaune is fantastic, and Bourges is too neglected by the visiting public. The Abbaye de Fontenay takes you further north, near Montbard. From there, the eastern end of the Loire Valley has Chambord, with Chenonceaux not far. Then a stop in Chartres to see the magnificent cathedral.
A different journey takes you through the Dordogne instead of Bourgogne. Go through Albi on the way, then Sarlat- le-Canada, Lascaux, Font-de-Gaume, Rocamadour, Castelnaud. A first stop outside of Marseille on your way to the Dordogne could be Nimes, with its Roman arena and proximity to the Pont de Gard, the Roman aqueduct.
Bonne journee!