Hello Frances
1851 England and Wales census shows James Henry Cain (age 24, master cordwainer), visitor at house of John (age 34, joiner) and Sophia (age 32, dressmaker) Blackburn, 15 Bold Street Stretford, Manchester. All 3 are IOM British subjects. J&S have 5 children: Elizabeth 10, Sophia Lane 8, Catharine Hannah 5, John James 3, Martha 5 mo, all born Manchester. Lodging are IOM British married couple William (21, joiner) and Radcliffe (28, dress maker) Radcliffe.
I can't find Elizabeth Blackburn in IOM in 1851, although I do have her marriage cert to James in 1853. The only one that makes any sense in the Manchester area in 1851 is described as a lodger in Providence St, Hulme, not far from Stretford, in the house of some English-born Blackburns, but the age (19) is wrong for her, and the census states she was born in Hulme. On the other hand, when they married, their address was Ward St, Hulme. If there's a chance that the birthplace was wrong ......
It is likely to be difficult to trace the Stretford John Blackburn back to IOM given that they will have moved to England before 1841 census.
I wish you well, and sorry I cannot find anything at present more helpful.
Will try again and see what turns up.
Good luck
Dave