The George Cains I have in my tree states his birthplace as Ippollitts in census returns, and his birth date can be calculated from similar sources as 1792 +/- 1 year; he was an agricultural labourer. By 1816 he had moved to Edmonton MDX where he married Ann Harris on 15 December (this marriage is in Boyd's index and the West Middlesex marriage index), and over the next 15 years the couple had 7 children baptised in Southgate and East Barnet.
The Ippollitts parish registers show baptisms for two boys baptised George Cain(s) between 1719 and 1850. One is in November 1792, son of Thomas & Sarah (Thomas Cains & Sarah Saunders were married there on 11 April 1774); the other is on 22 April 1798, son of Edward Cain & Elizabeth (Edward Cain & Elizabeth Barker were married there on 26 Jun 1797).
With this information it seems most likely to me that "my" George Cains who married Ann Harris was the one baptised in 1792.
I've been unable to find the marriage to a Mary Stratton that you mention in any source I have access to - can you let me know the source for your information, and any further details you have?