The previous answers are right, use Michelin, the AA or even the french autoroute site http://www.autoroutes.fr/.
Main thing I would say is that having driven up and down France using various routes for years, RN are much, much slower and tiring to drive on, especially going your distance. You end up behind lots of trucks and tractors and getting stopped at every roundabout/ traffic light in every village on the way. Yes, there are some by-pass roads but it is probably still twice the time and twice the pain. And if you are in a UK car (coming from Calais right?) then good luck overtaking by craning your neck over the passenger seat to check the road and then looking in the mirror to ensure you aren't being cut up all at once or asking your patient partner "is it clear?"...scenery is nice though.
The autoroutes are generally fairly quiet, very fast and frankly boring but they work and the Aires (road-stops, they usually alternate between petrol and just toilets and parkland) are very clean and tidy compared to the UK.
You pays your money and takes your choice I am afraid.
PS regardless of RN/ Autoroute, I always attempt to avoid Paris since it can take 2 hours to get round. Your route would be east of Paris anyway I guess.