Every winter, most great lakes trading vessel tie up for the majority of the winter, generally from Dec 28 until March 25 or the likes (when the Seaways is closed).
During this time all vessel are required to have a competent person aboard at all times for safety and security, and carrying out small tasks. The vessels tie up all along the port of the lakes around central Canada. Its a lonely existence but some might enjoy this. The pay I am not sure and probably depends on vessel, but in the low 100$ per day. Usually this is done by one of the ship's engineer, but sometimes they are not available.
If you are legally allowed to work in Canada and are interested in this type of work, I encourage you to contact the various ship operators in the area. In particular, you can contact VShips at firstname.lastname@example.org
to express your interest.