on what do you base a Manx origin - Cain(Kane) is also an Irish name and many from Ulster went to USA in 1720's as dis even more from southern Ireland into the older states - there are 2 Barnabas cain(e)s in record - one bapt 1763 in Malew s/o James Cain + Eliz Tyldesley matches well the age at death of the Barbabas I described - the other is s/o John Cain + Isable Skillicorn bapt in 1766 in Marown

however in 1739 ballaugh parish reg is a bapt of Jane Cain d/o Barnabas 'who now lives in Dublin' - he may be the one you seek ?