If the weather really turns out to be awful, prefer Marseille over Aix because there is a lot more (sheltered) stuff to do.

>> but yes not recommended in rough weather -<<

So you recommended it why?>

Read what I wrote - could be rainy and not rough.

And this up-to-date weather report for Cassis hardly has a rough storm forecast but only one day OP will be there with rain.

Update: Thank you for all the tips. The weather was wild but we came to Cassis to hike. Wind and torrential rain but it cleared and we walked around the water photographing huge waves hitting the lighthouse and rocks while things dried out and then managed to get over and hike the Calanques for four hours in absolutely perfect weather. Cool and sunny. Even saw a wild boar. Thanks for all the help. We are in St. Remy now (torrential rain last night) but perfect day today. Just three more days and I have not shopped and bought gifts yet to take home.