From the Govt of Canada website:
Fully vaccinated U.S. citizens and permanent residents and French citizens and permanent residents of Saint-Pierre-et-Miquelon (SPM) are eligible to enter Canada by boat for discretionary purposes and can come on land, anchor, moor, or come alongside another vessel in Canada. However, they must:
1) be asymptomatic;
2) have a valid pre-arrival COVID-19 molecular test result taken in the U.S. for U.S. boaters, or in SPM for SPM boaters (antigen tests are not accepted)
3) submit their mandatory information via ArriveCAN, including proof of vaccination in English or French (both vaccination doses, if applicable), and a quarantine plan; and,
3) be admissible under the Immigration and Refugee Protection Act.
Fully vaccinated U.S. citizens and permanent residents must also:
reside in the U.S.
be travelling from the U.S.
Important: All boaters who land on Canadian soil, anchor, moor or come alongside another boat in Canadian waters must report to the CBSA and are subject to all of Canada’s entry requirements.