If there is no specific reason you want to see Marseille, my suggestion is to just drive nonstop from Avignon to Eze, have the luggage ported up the hill and the car parked, and then start enjoying the coast. The south is notorious for items stolen from cars; if you can't put everything out-of-sight into the trunk, even an umbrella, don't stop. Your hotel is high quality, so it will offer a lot of services and information that will help you get from point A to point B. In addition to all the places people have mentioned, you should look in a south of France guidebook.
By the way, I am a fan of Marseille, having stayed nearby for six months and gone into the city 2-3 times a week. But unless you have a specific objective for getting off the autoroute and visiting with a trunk full of luggage, it may not be worth your time.