I'm on the ferry right now coming back from a trip (flew to Marseille and rode back to Le Havre via the Alps, then Burgundy, then the rest).
Between Mâcon and Buxy, in the Saone-et-Loire department of Burgundy, there is a converted rail line that is nicely traffic-free for about 60kms or so. I used it a week or so ago and stayed at a good campsite in Cluny about 25kms north of Mâcon.
I'm not too keen on Voies Vertes (as they call their ex-rail-line bike paths) as they tend to be a bit flat and boring, plus the view is usually blocked somewhat by hedges, so you don't get to see so much of the countryside as you would do on a country lane.
Having said that, they're nicely free from cars and the (relative) flatness lets you cover ground quickly between towns, if you're more interested in towns than the country.
I also travelled across Champagne, from right to left, a couple of years ago and thought that the wine-y valleys were lovely, but the rolling agricultural part a bit same-y after a while.
Visit Epernay as it's a nice place (cheap campsite close to town centre and near a supermarket). When you're there, you absolutely must do a tour of the Mercier Champagne wine-cellars. You go on an underground train 80m below ground and go through wine storage tunnels that have (literally) kilometres of champagne bottles stacked at the sides. Pretty cool.
