Traffic in the Montreal area is quite bad specially because there is a lot of road and bridge repairs in the area.
Your best bet would be from Renfrew to drive on hyghway 17 to Ottawa then take 417 east towards Montreal. Then once you're in Québec road name changes to 40.
Continue around Vaudreuil Dorion where you will be able to take Highway 30 and cross the St. Lawrence River on a new bridge ( toll ) opened approx 18 months ago. Then continue on 30.
This new bridge is not shown on Microsoft street and trips but look a Google Maps you will see it.
If you wish to stay in the Montreal area, there is a '' camping '' ( more a parking area, but there are some sites with electric and water, and other sites without services but you have acces to a dump station, and water. From there you can cross to old Montreal using a ferry located right next to the camping. This campground is right next to the local marina and you have some sites with a view to downtown Montréal alongside the river.
For more informations : Sogerive Halte VR RV Longueuil | A Campground near Longueuil Quebec
Also from Montreal to Québec City, drive on highway 20 to the south shore of Québec, On the city of Lévis, there are 5 to 8 campgrounds close to the City.