For Province of Quebec's marinas, you should download this bilingual guide:
Nautiguide 2023 - Nautisme Québec . Very useful with all the relevant information for each marina.
Once you'll get out of the St.Lawrence Seaway in Montreal, I would suggest a stop at
Old Montreal Marina . It is a convenient base to visit downtown Montreal. Avoid
La Ronde Marina, it's pricey and noisy next to an amusement park. Still in the vicinities of the exit of the St. Lawrence Seaway, you should be able to refuel at
Longueuil Marina.
From Old Montreal to Sorel/Tracy, this is a 40 n.m trip. In Sorel, if you want to stay there (not much to see in the city...), you can stay at
Marina de Saurel (refueling possible). In this region, the interesting thing is all the islands. Many boaters choose to explore and anchor among these islands.
If I were you,
I would extend my trip to Quebec City if you have the time. It is 100 n.m. east of Sorel and is worth the trip! Along the way, you can stop in Trois-Rivières where you'll have the choice of 2 marinas,
Marina de Trois-Rivières and
Trois-Rivières Yacht-Club. The first is well protected, has a mechanic and a small chandlery on site and is said to be opening this year a brand new restaurant. This marina is located within a large municipal park, The second is less protected from the waves of commercial navigation on the St.Lawrence River but is closer to Trois-Rivières downtown. Refueling is possible at both marinas.
70 n.m. from Trois-Rivières, you will find
Quebec City. It is a spectacular city when seen from the St. Lawrence. Stay at
Marina du Vieux-Port. You'll be next to Quebec's Old city as if you were in Old Europe. Plenty of restaurants, galleries and memories. Refueling possible in many places around Quebec.
Bienvenue chez nous!