Are you looking for the family of the John Cannell who was recorded as from Lonan when he married Christin Christian of Ballafayle, Maughold, in 1741?

The Radcliffes don't give any information about him, and I have only his probable burial entry: John CANNELL, Ballafail, buried Jan 25 1791. (No age)
This was only a couple of years after he made that marriage agreement which you transcribed: http://www.iomfhs.im/lawsons/twill/1807_018.html

As he married in 1741 his probable bapt date would be before 1722, and your John Cannell 1726 Lonan will looks like a possibility to be his father's. I couldn't see a likely John Cannell bapt there, so perhaps the family moved there from elsewhere? There are also:
CANNEL, Ann 1775-1 Lon A 2 0106227
CANNALL, Elizabeth 1724-1 Lon A 3 0106212
CANNELL, Isabel 1709-3 Lon JAMESON E d 0991649
CANNELL, James 1736-3 Lon E d 0106374
CANNELL, Thomas 1733-2 Lon E d 0106373
CANNELL, Jony 1737-1 Lon CHRISTIAN A 3 0106216
[From Brian Lawson's website.]

Good luck!

Sue