some more info: we have an especially wet summer here in Quebec ( I live in Qc City, but everywhere it has been really damp), so be prepared to have some rain on the road. I don't wish you some though! On road 132, which is the national road that goes along the St-Lawrence, be careful cause at some places, the shoulder gets pretty thin to roll on. Usually drivers are somewhat aware of cyclists there, and pay good attention. But still, it's North America
Campings should not be a problem: most of the vacations are almost over, and this is not the most crowded place in Quebec in all summer. For the sleeping bag question, I usually get along with a bag around 0deg (32F), and it's perfect. You can have 5-10 deg nights at this season, usually. Not much big heats (they have passed between rainy days). Most of the time you will have a west wind on your back, but it's common to see easterly winds pick up with the bad weather. Be prepared for a constant 10-20 km/h of wind almost at all times. Mosquitoes should not be much of a problem either, as it is usually windy, but as we had an horrendous wet summer, you can bring along a little tube of Watkins stuff (lots of place where you can buy it). It's DEET (28), but it works even in James Bay (I know, i've been working/canoeing there).
Road stops: if you follow the north bank of St-Lawrence and want to go to Matapedia, you will have to take a ferry, something like Saint-Siméon to Rivière-du-Loup, or Matane/Baie-Comeau. But be prepared for LOTS of hills on the north shore! Great scenery but not very accomodating for cyclists since there is a lot of heavy traffic there. I mostly recommand you get on the south shore from Lévis (you can take a ferry from Qc City), and follow the Route Verte (http://www.routeverte.com
) or the 132 road. You WILL have to stop in Saint-Jean-Port-Joli nice little village with a penchant for wood carving), Kamouraska (for the great bakery there: Niémans and Poissonnerie Lauzier), and Trois-Pistoles for the famous cheese curds at La Fromagerie des Basques. Try to camp one night in Saint-Andre-de-Kamouraska (a great climbing spot; incredible sunsets) at the SEBKA.
Matapedia valley is a little more isolated and wild but you will find enough villages with grocery stores around so you won't have to carry a week's worth of food on the bike. Get ready to carry some spares bike stuff as there are almost no bike shops there but you will find one in Amqui and afterwards in Baie des Chaleurs area.
I know a little less about all the Gaspe peninsula (mostly been there by car, or ski touring) but lots of little villages there and around. Beware of the wind and the long distances you could have to put between two places!
That's it for me now. Hope you will enjoy your trip, it's a very great and pittoresque region! Hope this all helps!