Batman1, wherever you go on your jaunt, you'll probably be covering quite a large distance across a big country. My only tip would be to try to keep it simple on your first trip. That is not to suggest that it's not fun, I'd just try to avoid a mass of left, right, left, right, right changes in direction down every D road you can find. Why? Because you'll probably find it will take you longer than you think.
For example, Cherbourg where you are starting from to near enough Bordeaux, where my simple suggestion of following the Lot river starts is 700 kms (direct via the fastest routes) call that 440 miles. To put that distance into perspective, Lincoln to Penzance is 350 miles, whilst it's 410 miles from Lincoln to Aberdeen, so still 30 miles short. Then consider that somewhere during your seven day jaunt you (or your long suffering pillion) might like a day off the bike, or a long lie in one day or a full afternoon just picnicking by a river. You have now lost a full day's riding distance or at least half a day, but hey, it's a holiday, too. Just ask yourself if you were riding to Aberdeen would you necessarily set off to do it in a day, starting at 10 AM and finishing at 15:30 and, if you did, would you set off taking every small road you could find?
A very good map to get, is Michelin's 726 map:
I cannot recommend it highly enough. Why? Because it is designed for exactly the sort of trip you might be making. It strips out all of the minor detail, leaving just the main towns, major roads and.... most importantly.... Michelin's suggested Bis 'Tourist routes' (coloured green) designed to take travellers from A to D via B and C, reasonably smoothly but not hurtling down every motorway. Are they always, "Great roads, mate"? No, but they are certainly not all bad either. We hear lots of advice on this and other sites about simply following the yellow D roads that Michelin have designated 'scenic' on their other maps by lining them in green. Yes, they are often very nice but are not always a great way to go four hundred and fifty odd miles (in perhaps a day, in an extreme example) from Cherbourg to Bordeaux in order to reach the river Lot, to start the main bit of your holiday, if you have never done it before.
I don't want to make it sound awfully dramatic or some epic jaunt. It isn't. People of all sorts and ages, on bicycles, to motorbikes, to cars to vans to trucks have bumbled and bimbled and hooned across and through France for years, arguably since the Romans. It's easy to do, I promise you. Just think about it a little, that's all. For instance, there is a good chance that someone in this thread might recommend you stop to visit Oradour-sur-Glane and / or see the Millau Viaduct. Both are very worthy suggestions but will take time, say maybe half a day each by the time you've finished. That's fine but then look at a map and see that from one 'must do' site to the other (direct) is 340 kms or 210 miles, useless if you need by then to be hurtling your way to your ferry
in the opposite direction as its loading doors are closing.
I have come up with a suggestion, Wessie has too with a good idea. Others will for sure, as you have lots of time. That's great but maybe inevitable, not least as you have seven days and France is a huge, very varied area. You could, if you wanted, spend all your time bimbling around Brittany and Normandy on the D roads, see the WW2 sites (if that's your - and your pilion's - thing) and still do all the D roads near enough back to your ferry and home. That would still be good but you'd not come within several hundred miles of Oradour or Millau or the river Lot. That wouldn't matter as all three will still be there next year; let's hope we all are, too.
My last suggestion might be to have a look at RiDE magazine's website and their pre-made touring holidays, which sometimes start from the Channel ports. They are pretty good, not least as they are often broken down into reasonably well thought out daily mileages. Yes, before anyone says it, they are a compromise and, yes, it's possible to ride 500 or even 1000 miles in a day for nearly 20 days on the bounce if you want to. But that's not the point of the magazine's suggestions nor their compromises to cater for all sorts of riders, of all sorts of abilities, on all sorts of bikes. Just because a bod rides a GSA with TT panniers, stickers and a one litre plastic jerrycann of fuel (to top-up the 33 litres of fuel he's already carrying, to get him that extra 10 miles to his bikermate safe B&B, where they speak English and do bacon and eggs, none of that foreign shite, mate) doesn't mean that he goes miles and it certainly doesn't mean that he doesn't agonise over whether the hotelier is going to be friendly or whether his awesome steed will be safe at night out on the street in some village hamlet. Similarly, the bod on the outright sports Ducati, who's ridden all the way from Finland to the river Lot, is not necessarily some motorway bashing, "50 miles and I have to stop cos me arse and wrists is killing me, mate" nancy, either.
Here's RiDE's very good ideas for France:
http://www.ride.co.uk/routes-1/the-ride-guide-to-france
Or see if there might be some ideas to adopt and adapt in:
http://www.ride.co.uk/magazine-routes/routes-from-ride-magazine