I'm not sure if it's the same Benjamin Crossman, but there's a record of one who immigrated to PEI from NB in the 1790s. He was married to a Zipporah... The reference is here (but I don't know where that info came from)
http://www.islandlives.ca/fedora/ilives_book_viewer/ilives:1... on page 13.
So... I don't know if perhaps Eunice died, Benjamin moved from NS to NB, married Zipporah, then continued to PEI. Or if Eunice and Zipporah are one in the same (maybe she went by a middle name?).
I don't know if this is old news for you, but I thought I'd share.