ferryman.ca
The Montreal area supports a number of small ferries for pedestrians and bikes, known as navettes fluviales, or river shuttles. These operate in the summer months only, and even then many are restricted to recreational timesweekends, holidays and specific dates. They are run by local boating operators and supported in part by the recreation budgets of local municipalities.
These are the ones I know about, as of summer 2022, although I have yet to try any myself. The services tend to change from year to year depending on how successful they are. Check the websites of the operators linked below for up to date information.

Route operated by the

Les CèdresThe Îles-de-Saint-Timothée regional park

Routes operated by

Notre-Dame-de-l’Île-PerrotPointe-des-Cascades
Notre-Dame-de-l’Île-Perrot Beauharnois
Notre-Dame-de-l’Île-Perrot Sainte-Anne-De-Bellevue
Lachine Châteauguay
Boucherville Montréal Vieux-Port
Pointe-aux-Trembles Montréal Vieux-Port
Longueuil Île Charron
Montréal MercierBoucherville
Montréal MercierÎle Charron
Boucherville Île Grosbois
Pointe-aux-Trembles VarennesRepentigny

Routes operated by

LongueuilÎle Sainte-Hélène
Montréal Vieux-PortÎle Sainte-Hélène