I found Neil Simpson in the 1881 and the 1891 Canadian Census as one of the children of William and Helen Simpson. I was unable to find him in the 1901 so far. His mother is by now a widow, and listed as the head of the household, and she is left with the 3 youngest children at home.
To get an easy overview of all the Canada Census information, I added all the data in Canada Census Overview Charts
I did find Neil in the Public Archives in the Marriage Records.