Tryin to decide between marseilles/ provence or cannes/ nice traveling May early June.
I want a trip filled with exploration, good food and a little beach time. suggestion thoughts?

What are your more specific interests--historic sites, museums, perched villages, markets?

Nice would be my choice out of those three areas.

Provided you do have a car: Marseille/Provence! Count one day to explore Marseille, eat bouillabaisse, then explore along the coast (Sausset les Pins, Carry le Rouet - nice little beaches and authentic seafood),drive one hour 15 min up to Vaison la Romaine (lovely big Provencal Tuesday market, best restaurants: Bistro d'O and new and very good: L'Auguet) have a look around the villages of Roaix, Sablet, Séguret, the wine villages of Gigondas, Vacqueras, Chateauneuf du Pape, then on to Avigon (Pope's Palace and the famous bridge and, if you are into contemporary art, the fantastic Collection Lambert) - the possibilities are endless and you'll be in real Provence and not in overcrowded coastal tourist traps.

Just to clarify: Provence is a huge area, and it includes Marseille and Nice.