Isabelle's maiden name is on the regsitration of death of their son, John Smith McGlashing. See:http://archives.gnb.ca/APPS/GovRecs/VISSE/141C5.aspx?culture...
It also has both J. Smith's parents born in Westmorland Co., which, at least in the case of John, Sr., seems unlikely. It seems that J. Smith's son, R. L. (Ralph Lester) did not know (in 1921) the shipwreck story, which is sort of interesting.
As to Isabella Seaman being b. in Westmorland Co., that seems a bit doubtful as well. I see no Seaman's in the area in the petition and grants indeces.
There is a query at:http://boards.nbc.ancestry.com/topics.cemetery.canada.newbru...
that might interest you. Also:http://groups.yahoo.com/group/nscumber/message/18718
She is also given as Catherine Isabella Seaman.
Perhaps a marriage record in PEI? Also Westmorland Co. marriage registers start in 1790 (on microfilm F-1671) and another from 1812 on F-15493. May be worth a look.