I cannot really help, but here are some possible leads:

Thee 1881 census has an Elizabeth C. Gabrielson, married and born in Ireland. A William T. Shannon, nephew, is living with her. By elimination, that means that John Q. married Elizabteth Cain.
The 1881 census also has a John Qualtrough (52) and Elizabeth (52) in Liverpool.
A Thomas (21) and Theresa (17) Craine, nephew and niece, both born in Liverpool, are living with them.
Thomas is a "Shopman Bread & Flour"
The IGI shows a Thomas and Theresa, children of Robert Cain (no "r") and Ann.
It is possible that these are the nephew and niece of John, and that the census mistakenly added the "r".
The 1881 census also has a Robert (43) & Ann (43) Cain in Walton on the Hill, both born in Douglas. Robert is a baker.
In the IOM census of 1841 Douglas, district 8 page 3, entry 12, there is a Robert aged 3 and an Elizabeth aged 11.
They were living then with Edward and Elizabeth (née Christian) Cain.
I hope that this helps.
Bruce