The way to do serious distances over France under VFR is by following their "airway" routes; typically these are at FL065 or higher. They avoid the mass of military airspace that covers much of France, and you get easy clearances through any Class D enroute. Nav-wise one obviously flies with a GPS but these routes are based on VORs anyway which is handy as a backup.
The drawback with flying at such an altitude is that one can get snookered. If flying from the UK to France, one needs to be able to make a VFR arrival, so better be very sure of the cloudbase at the destination! If flying from France to the UK it's a lot easier because, assuming an IMC Rating, you can fly VMC on top the whole way and land with an instrument approach in the UK.