I have some time after touring Provance and was going to head to Brussells via the above named French cities.
Are all these cities deserving more thatn a day to tour?
I was thinking of spending a night Plus a day at each.
You're starting in Provence and heading to Brussels. Marseille, Lyon, and Reims are in a straight line back up from Provence to Brussels--but Nice is the odd man out way to the east of your line to Brussels in terms of travel time. I'd eliminate Nice from the list for this reason.
If you're an art lover, spend several days in Nice and use it as a base for short day trips. Outside of Paris, Nice and the surrounding area have the best art museums in France. Train and bus service along the coast is frequent and cheap. Bus service to hilltop villages is less frequent, but adequate.