Recommendations for a weeks cycling trip in France accessible by ferry from the UK?

I hate to say this but if you ride in Northern France you might as well just ride in Kent.

and I hate Kent.

Rubbish, less cars and better food in France for starters

You can't go wrong with any of the ferries really, though I tend to avoid Calais. Dieppe is best option if you want to head to Belgium, Ypres is a good trip (going via Westveltern).

I can recommend Cherbourg too, we had a lovely week cycling round there, coast is nice and some good sights inland too.

main dishes are actually ok too.
Cherchourg is a good base also, going around the peninsula is pretty cool, with some good sandy beaches facing west.

too much information anyway, let the guy have an adventure :)

All this talk of French ferry adventures has tipped me over the edge. I've just booked an overnight ferry to St Malo, from where I'm going south to my mate's place in the Vendée then up to the Loire and along it as far as Blois. I've done Amboise to Orléans before and it was wind-in-your-face drudgery, so I'll train it to Paris, then out to Gisors or maybe Gournay-en-Bray and take the Voie Vert back to Dieppe.

Are Brittany Ferries the only service arriving in St Malo?

Condor Ferries run to the Channel Islands from the UK and St Malo, which means you can also use them to cross the channel, optionally with a few hours on Jersey or Guernsey if you've never been.

The French coast definitively gets more interesting the further west you go.

For Belgium, Dover - Dunkirk is best.

Reckon this kind of thing would work as a long weekend trip in December? I have holidays to use and I'm struggling to find motivation to ride anywhere near London.

That would only be true if the UK exported enough fuckwit drivers to France.

Fewer cunts driving too.

Yes - likely to be milder by the coast so should be more pleasant riding than inland. Obviously, book last minute after checking the weather forecast for nasties, campsites won't be open so hotel or bivvy if you are hardcore, and an early start from the Dieppe ferry would involve quite a long, dark morning as the sun won't be up until about 9am.
Ferry schedule a bit restricted in winter so fewer options, but still plenty.