In reply to Phil1919:
There is a route that goes towards Dinan along the canal then on towards Rennes. Getting out of St Malo can be interesting as the main road out is a dual carriageway but there is a route I can point you at. The weather as someone pointed out can be quite cold at night so I guess just keep an eye on the forecast. The roads are generally pretty good for cycling and the drivers are mostly cyclist friendly, I tend to work out roughly where I want to end up at the end of the day then choose a route mainly based on the green roads on the michelin maps.
The whole area is great for touring and there are lots of cheap hotels around as well if you want a change. Not sure how many campsites will be open then as they tend to have a short season.
SteveD