The route roughly follows Faro,Huevla,Caceres,Bejar,Salamanca,Zamora,Burgos,Logrono,Pamplona,Bayonne. Have few worries working my up thru France. Thinking of going around June.
On my 2011 trip my outward journey went down the west coast of France from South Brittany, over the low edge of the Pyrenees (Ainhoa) to avoid the built up area on the coast at the French and Spanish border, then round (not through!) Pamplona. I kept inland, but avoided most big towns as far as Benavente (not far north of Zamora) and did a short loop into Portugal to Bragança.
My homeward journey went from Bragança to the Picos d'Europa, passing close to but avoiding Léon. I spent some time exploring the Picos, then crossed Cantabria and the Basque Country near the coast, passing through the outskirts of Santandar and the centre of Bilbao, then the built up area on both sides of the border that I had avoided on the outward trip. And back up the west coast of France to home.
Like Bikerwaser I also found that, in general, drivers in Spain were more cycle-friendly than in most parts of France, which is already reasonably good. But I didn't much like driver behaviour and traffic in the small bit of Portugal I cycled in, it reminded me of the UK.
Most of the roads I travelled on in Spain were lightly used, even some A-road equivalents, often because there was a motorway nearby that had taken most of the traffic. The exceptions in Spain were the few big towns I went through, and the Basque country near the French border - here the roads generally follow densely populated valleys with lots of heavy goods vehicles.
In France, traffic was heavy on some of the roads I used in the border area near Biarritz/Bayonne and on the road I used between Rochefort and Royan (I found a more peaceful alternative here on my way back). Between Royan and the border area, there are long stretches of dedicated cycle routes, some of them are a bit sandy though.
I avoided the St Nazaire bridge over the Loire estuary, this has a very narrow cycle track running next to heavy, fast moving traffic. I've cycled over that several times in the past between 1977 and 2003, but now prefer to make a detour for safety reasons and use the free ferry some way upstream between Le Pellerin and Couëron.
