Be careful about using a ferry in Canada. I read on another forum that they charge rv's by the foot, and the price was recently increased significantly.
On the Ferry from New Brunswick to Digby, Nova Scotia, they charge by the foot and then add a per person fee and I believe, a fuel surcharge. Their website is nfl-bay.com.
On the ferry from Nova Scotia to PEI, the fare is collected when you leave. We take the ferry over and the Confederation Bridge back. The bridge is $42 which is less than the ferry.
Both ferries transport semi's so you won't have any problem with size.
There used to be a ferry from Maine to Nova Scotia but last year it was discontinued.