I've just done the stretch from Toulouse on, through Auch, Pau and over the Pyrenees to Jaca, thence west to Puenta la Reina in Navarre. The French stretch was not well-marked in 2005, although locals were friendly and helpful. It is not used much by pilgrims and in September, 2005, I do not think that I saw a dozen pilgrims in as many days. The countryside is gently rolling and is a great walk, with lots of remarkable churches in the villages. I'd do it again in a trice.
Accommodation is easily available, but it is not pilgrim-specific. Hikers gites are quite common and pilgrim-friendly, and there are plenty of inns, b&bs and hotels. However, costs are greater than in Spain and pilgrims will need to be very careful not to spend 10-20E per day more than in Spain. As well, English is not spoken everywhere and you will find the capacity to operate in French will be very helpful indeed. Noe that many small villages have no facilities at all other than water, including cafés or grocery stores.
The Camino Aragonese, in Spain, to Puenta la Reina in Navarre is covered in that section of the Board.