Bad news for you but seems that the only ferry service between Nova Scotia and Portland is provided by "the CAT". However here are some resources that I've found:
http://explore.ca/vacation/gethere.shtml,
http://www.exploremaine.org/ferry/index.html#portland,
https://www.canadaferry.com/bokning/en/default.asp?secure=true,
I hope you can change your departure city, have a nice trip!
Regards - (2008-08-29)
