The extensive French military airspace tends to be inactive on Sundays, and perhaps Saturdays, and tends to be active on weekdays. The other day I flew to Biarritz along the west coast on a Sunday, through R31A1 etc.
However it is easy enough to establish whether a particular bit is active or not; just call the nearest ATC unit. If they don't know they will either find out or tell you who to call.
Contrary to frequent reports of unhelpful French, I have found them to be extremely helpful and courteous - though presumably they expect you to have similar radio manner to start with
Usually they gave me a Flight Information Service which turned out to be really equiv. to the UK Radar Information Service (with a squawk) and very efficient.
For France it REALLY helps to gave a decent GPS, with an up to date large moving map showing all the airspace zones. At times, when they are active and the cloudbase is low, navigating around them and in between them would be exceedingly difficult otherwise. There are plenty of NDBs and VORs but not enough, and very few DMEs! And IFR is not allowed outside the airways - or so the ATC told me!