On the "1789 schedule comprehending the Lots under Certificates in the District of Lunenburg," there are 8 Alexander MacDonells. None of them have the specific MacRail to their name, though.

In "The Old Eastern District..." by Pringle, Alex. McDonells living in Charlottenburgh in 1786:

1-Lot 9, 1st C, Fronting the Lake. Alex. McLaughlin and Alex. McDonell

2-Lot 12, 1st C, Fronting the Lake. There are two Alex. McDonells sharing this lot.

3-Lot 25 and 26, 1st C again. Captain Alex. McDonell

4-Lot 25 and 26, 2nd C From the Lake, Alex. McDonell.

5-Lot 12, 2nd C From the Lake, 2 Alex. McDonells again

6-Lot 14, C South Branch of the River aux Raisin, Alex, McDonell, shared with John McDonell

7-Lot 45, 1st C North of the River aux Raisin, Alex McDonell shared with Hugh McDonell

8-Lot 55, 1st C North of the River aux Raisin, Alex McDonell shared with John McDonell

I added the Alex McDonells that front the lake(the first couple on the list), although they would not be living near the Black River/River aux Raisin, if the were living on those lots. I think this should narrow it somewhat, although keep this in mind that not everyone on the 1786 map stayed in the area.