Canada's "Reporting requirements for private boaters" (updated 8/9/21) indicates that you can enter for fishing but cannot land, moor, anchor or come into contact with another vessel. If you anchor, disembark, come into contact with another boat or land you need to report and are subject to requirements including vaccination, a negative COVID test, quarantine plan and ArriveCan reporting. The website specifically mentions that "Travelers engaged in transit or loop movements are not required to report to CBSA." Loop movements include fishing.

Reporting requirements for private boaters