Shall I have any problem with the Marseilles accent ?

You will have no problem at all. Every French speaking country (and every region in each of these countries) has its own accent and you will discover them with pleasure. Furthermore, Marseilles is a big cosmopolitan city and you will notice people speak with hundreds of different accents or no accent at all. This is the case of CIPEL teachers who come from all over France (including Marseilles).