In a day, with an early start and no flower pressing en-route, I would go:
Troyes
D944 Chaource
D944Tonnerre
D905 Ancy-le-France
D905 Montbard
D980 Semur-en-Auxois
D980 Precy-sur-Thil
D980 Saulieu
D15 / D4 / D981 Autun
D994 Toulon
D994 Digoin
D982 Marcigny
D982 Roanne
N7 / N82 / D1082 St Etienne
D1082 / D620 Valence
M'way A49 Grenoble
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As an alternative (and probably quicker route) after Autun
Pick up the N80 / D980 on the diagonal to Macon
D1079 Bourg-en-Bresse
D1075 / D1504 Chambery
D1006 / D520 / A49 (motorwary, short hop)
Grenoble
All done from looking at an on-line Michelin map, hosted on ViaMichelin's website.
http://www.viamichelin.co.uk/web/Routes
What I did was ask ViaMichelin for the basic route. I then looked at how the start and end points related to each other. It was clear that the Rhone River (very big) and Lyon (France's second city) get in the way, the A6 motorway running down the middle. To the east of the motorway the map shows it gets very congested, not least as the geography of the region gets squeezed between the Alps and the Rhone. The trick was then to find some D roads ('Great roads, mate') that would still get me near enough to where I want to go, without touching the Atlantic coast, avoiding too many left-right-left niggardly turns down small roads and (most importantly) still allow me to crack on. I have ridden both routes several times in both directions, along with other variations on a theme. Get your maps ready......
Impossible to do without a decent map.