Can't find Thomas on the 1851 so far but I have just found this:
1851 Etobicoke, York County
William McGill, 35, Cooper, b. Scotland
Sarah, 30
William, 10
John, 8
Jane, 4
David, 1
all except William b. Upper Canada
Thomas McGill and Jean Burgess did have a son, William, b. 8th July & bpt. Parton on 11 July 1816
I think it's worth following this family through. There was a tendency in the Burgess family to name their first two sons William and John.
Gadget