Well, I always thought that the old road through Abbeville was especially nice. I used to like passing the old Castle ruins and then on down the side of the river/canal. I also then used to really enjoy the old road from there to Rouen, with its tree lined prettiness as it cut pretty much dead straight across the farmland. Much better than the new dual carriageway most seem to use (I remember all the chaos caused whilst that was being built
).
However, if you wish to avoid Rouen, you could go from Abbeville to Amiens along the side of the waterways (N235). I have never done this, but it should be a pretty scenic route, and there is a great Cathederal in Amiens.
From there how about an overnight in Versailles? Then the following morning overland to Alencon and a traditional finish to the journey from there. Or you could go straight down via Chartres and use the quiter east side of Le Mans for your entry.
Hope those give you some ideas.