Just saw some recent news on the Maine to Nova Scotia that you might be interested in. As in 21 June, the ferry from Maine is not expected to start service until after 18 July. The apparently are having some problem with certification of the terminal in Maine and one article questioned whether it would be solved this summer. You can check on any later developments and make reservations at the site below. We could not get a reservation for our Axis on the St John ferry for the day and time we wanted trying a week in advance. They only take so many large vehicles and a lot of tractor trailers use the service.
https://www.ferries.ca/