hey,
Just some hi-lights/low-lights, to consider:
you can skirt down the west side of Paris, fairly close, on reasonable roads for cycling by going through Dreux.
Orleans is a favourite place of mine, so I tend to cycle there when I'm near. The municipal campsite at Olivet (5km south of Orleans, an easy cycle) is justifiably full in summer (it is a fantastic site) so booking is essential. The campsite in Orleans, by the river, is acceptable but nowhere near as good. Hotel de l'Abeille in the centre of Orleans is a very nice, and not so expensive, hotel in an old town house, and if you turn up by bicycle they'll give you a cool drink while checking in; very bicycle friendly.
The centre route, I've found, is less touristy, which I prefer. That means eating (properly) local, during fixed hours (without tourists they serve the locals and then close up) in bars and truck-stops (not like our truck-stops!). I've had the best, most interesting food this way.
Albi is a cultural centre (Cathars), so there's lots of interesting things around there. Just south is the road from Mazamet to Carcassonne, which is really scenic and well worth the initial hill.
Bordeaux is quite far out of the way, though chosen because it's flatter. I don't think that justifies going that way, is it's not a particularly nice route (heavy traffic too). Canal du Midi is, in my experience and opinion, quite boring; you just sit on a straight canal for day after day without being able to see over the bankings. They have also taken out the trees (or are about to) because of disease, I think. Lyon I liked a lot, and it was another very bike friendly city.
The coastal route to Barcelona is one I'd avoid, having done it once. After a few weeks in France, pleasantly meandering and being welcomed as a cyclist, the Costa Brava is not a great place to be (tourists, traffic, HGVs). Although it means a few hills (by this time that won't be a problem) the route through Foix, Puigcerdá and to Ripoll is much, much nicer. There's also a railway on that route, should you prefer to let the train take the strain. You'll also get a much nicer entry cycling into Barcelona this way, as Barcelona hasn't been able to spill westwards far as it has northwards.
Regional trains in France and Spain are very easy with a bike, so keep that in mind. I've cycled all over France and I really prefer the hilly areas (Massif Central, Ardèche, etc). But to get to Barcelona I preferred most the central route along the lines of : Calais, Dreux, Orleans, Montluçon, Figeac, Albi, Carcassonne, Foix, Puigcerdá, Ripoll, Vic, Barcelona. If you really didn't want to cycle up the Pyrenees to Puigcerdá, I'd recommend the train up from Foix rather then the Perpignan route.
I don't plan a route in advance, I just pick up a map showing D-roads (our B-roads) and make it up each morning over a coffee/croissant. It's also worth, in advance, working out what sort of food keeps you going (protein/chicken-based dinner means my legs are brand new in the morning for example), as eating the right things makes a big difference. That's more trial and error though, but you've plenty of time to try out a few days on the bike.
I travelled up and down to Barcelona by motorbike for years (I freelanced down there), but it was not until I cycled that I really felt immersed in France and realised I'd missed out on a lot of the culture. Traversing the country (rather than a 2 week holiday) really puts you in the right mental frame of mind I think, and the French give you an extra bit of kudos for it too
sorry to deviate off your bike-choosing thread.
