Highway 132 is alright, and since you are headed westbound on the shore side of the road, it will be easier for you to turn into the parts of the Route verte that hug the riverside without having to cross the highway. The only hassles will going through the larger towns like Montmagny, but it is really straightforward except for the heavier traffic. Of the villages on that stretch of the south shore, Kamouraska sticks out in my memory. There is a great bakery
there near the church, nice place to stop for a break.
Up along the Saguenay River, The village of Sainte-Rose-du-Nord is quaint. It is a bit of a descent into the fjord (therefore a climb out) from the highway but if you need a place to stay in this area it may be worth it. Not sure about motels here since I camped, but I remember an awesome meal in a a restaurant called Au Presbytère
Tadoussac is nice. If you are lucky, whales sometimes swim as close as a hundred feet from the shore. I saw a few belugas standing in Pointe-Noire (in Baie-Ste.-Catherine across the river)