From Nice through the edge of the Alps to Grenoble it more or less marks the south-western boundary of these Virtual Alps pages, though there are a few notable locations between here and the Rhone Valley, such as the Vercors region, the Signal de Lure and Mont Ventoux, and perhaps best of all, the Grand Canyon du Verdon.
We avoid cycling on the Route Napoleon which has several very tough climbs and is an N class trunk road so a lot of motor traffic is inevitable. Although on the few occasions we have used it, it's never seemed at all busy, strangely.
A good tip with any unavoidable main road in France is to ride it around midday if possible, lunchtime is very important to the French and traffic eases off for 2 hours or so between 12:00 and 14:00.
A good stopover town is Sisteron.