Much of the Eurovelo 3 route in France does not maximize scenery, IMO. The portion between Orleans & Tours is nice, however. I don't know the EV3 route between the Belgian border and Paris. I do know that the landscape due north of Paris toward Belgium is just about the only boring section of France, scenery-wise. So hopefully the EV3 route approaching from the northeast is somewhat better.
I woud not continue to follow the EV3 route after Libourne (just northeast of Bordeaux). Bordeaux is not a must-see city, IMO, though it's not at all a bad place. Rather, I would start to head east up the Dordogne river. That has some of the nicest scenery in France. Initially from Libourne you'd be riding through some of the famous Bordeaux vineyards, but as you get further up the river, the scenery gets much more dramatic. You'll be riding through a limestone gorge. There are lots of beautiful villages, castles, caves, & gardens. 100 km/day is a lot, and in this area, there are many places you can visit, so consider slowing down a bit and visiting places. I would advise then heading south passing through Albi, Castres, & Carcassonne. In the event that you were planning on riding the Canal du Midi, my friends & I hated it. The scenery was boring compared to what we had biked through in the Dordogne & Lot valleys, and the surface was mostly very rough pavement.