Linda,
Wow! Thanks a lot for all that stuff. I will have to see how what I already know fits with what you have found. Based on ones I have seen for other places, I doubt the actual documents have much more information than you have quoted, but I will try to get my hands on them to make sure. It could take a really long time to have land petitions granted. One of my McLeans from the east coast of Cape Breton (Kennington Cove) applied for a grant in 1841, just before he got married. It wasn't actually approved until 1852 -- the first one for that district!
I agree that being next door to each other might indicate that John was closely related to Hector, but I'm not convinced that if he was only 17 he wouldn't still be living at home if he was the son.
My reason for thinking that John was Hector's nephew is that John and Flora called their first known son Donald, which, in the Scots naming tradition, would indicate that John's father was called Donald. In the same tradition, the second son would be called after his mother's father. John and Flora's second son was Hector, and we know Flora's father to have been called Hector. If John's father was called that, I would expect the first son to have been Hector, and the second boy to be called John, after his own father.
I had a look at an on-line transcript, which also shows a William McLean living beside John and Hector. I think this was probably the William McLean who was married to Hector's daughter. (We aren't sure what her name was but think it might have been Flora or Mary. McDougall calls her Miss McKay.) William McLean and "Miss McKay," not having any children of their own, are said to have been the source of the 900 acres farmed by John McKay and Flora McLean.
I guess the next step is to try to sort out the land records, in case there was more than one John McKay.
Myrna