Found another marriage for George. Likely the same one you have.
7 Feb 1877, Clarence, George Simser, 26, b Osgood, living Clarence, married Kattie McLeod, 22,Cambridge, Cambridge, d/o Malcolm McLeod and Christie McCrimmon, witn: Sarah and Leah McIntyre both of Clarence.

Could Kattie McLeod be Harriet? Maybe registrar heard Kattie instead of Hattie?

Here is a Harriet [ 2 actually] on 1861 census Russelll.
McLEOD
Mal, farmer, Scotland, 47
Chris, Canada West [Ont], 38
Harriot, CW,18
Mal, CW, 15
Jno, CW,12
Don'd, CW, 11
Cath, CW, 9
Harriet, CW, 7
Nor?, CW, 5
Alex, CW, 3
Christy, Scotland, 76, widow,

1871 census Cambridge Russell.
The McLeod famiy is on there,even old Christy at age 90.
Harriet's age is 17.

Then there is the marriage in 1911 to Fanny.
I think he was only married twice and didn't have any children with Harriet.