Marseilles to Nice by car

After many years without setting foot in the village of Cassis proper, I went back yesterday and realized that there is actually very little to do there!
Even for hiking it is not the best base, because the main trailheads are closer to Marseille.
It is still a good place to stay if you find a hotel you like, but I would also look at hotels in the southern districts of Marseille (Prado/plage, La Pointe Rouge, Montredon, Mazargues, Les Baumettes...) as you would have better access to Calanques hiking and to Marseille restaurants + other attractions. Marseille traffic is not great in the center but it is OK in the southern half.
La Ciotat is also a good alternative; the Best Western there is great with a rooftop pool even (French Best Westerns are usually very good).

By the way, when parking at Calanques trailheads, car break-in is unfortunately endemic at Col de La Gineste and the Logisson, along the main Marseille-Cassis highway. Use other trailheads such as Luminy campus or Baumettes prison.

Further east, Sanary sur Mer is a lovely seaside town, more charming than Cassis in my opinion. Hotel Synaya is pretty good there. There are plenty of touring options in the area, but less good hiking.

Further east still, I am a bit less knowledgeable. There is great hiking in the Esterel massif, so staying close by makes sense: in St Raphaël itself, or perhaps more charmingly further along the Esterel corniche - but beware, the coastal railroad and the road are busy.

Important note: after 15 June, access to hiking areas can be restricted due to fire hazards, especially on windy days. The info on that is a bit piecemeal as it is managed by département (French administrative division), Google "accès massifs forestiers Bouches du Rhône / Var / Alpes Maritimes (the three départements you will traverse)" and translate as needed.

We spent six months in Cassis and found plenty of hiking. I belonged to the town's hiking club. My favorite was on the Sainte Baume mountain trails a little further east. In June, you have to start about 7 am. Follow this with a good lunch and a nap.

To clarify what I meant perhaps: there's a lifetime's worth of hiking trails within 50 km from Cassis. It is incredible in that regard! I am just questioning whether Cassis is necessarily the best base to access them, as I was quite disappointed by my visit yesterday. Highlight was the Bestouan beach with its clear water and incredible view of Cap Canaille.

And yes, I did not mention it because the OP said "coast", but the Sainte Baume is amazing too! Went up there last May and got...licked by salt-starved goats once at the top 😂. That memory will stay for sure.

The Esterel Massif does have some great hiking. Ste. Maxime is one possibility, Theole-sur-Mer is another. Another alternative is go to Porquerolles and the Port Cros National Park, just off Hyeres. You could stay there or day trip by ferry.