cruise stops

Your best source will be cruisecritic.com. They have multiple reviews of every port (and every ship). You can get an idea what your options are at each of your ports. You might notice the people at cruise critic tend toward cruise sponsored tours, and I'm the opposite. Once you decide your top sights, there's usually a way to tour it faster and cheaper by doing it yourself (or even hiring a local guide) rather than taking the cruise tour. If you like, cruise critic also has a roll call section for chats with people who will be on your specific cruise. They normally try to have an informal get-together on the ship and sometime organize private tours within the group.

The Luberon is about 1.5 hours from the Marseilles port by car. To us it is the best of Provence so it would be good for a tour. You could also take the train on your own to nearby Cassis which is very picturesque with restaurants and shops around the harbor. It's been a long time since I visited Marseilles. I only remember Chateau d'If which is worth a visit if you stay in Marseilles.

For a good idea of the top itineraries for each port stop, look at the tours your cruise line sells. You can usually pack in a lot more than any of them, though, because there's usually a lot of eating and shopping time included.