If your Peter Grant was married in Charlottenburgh I assume he was born there around 1800. Was his father named Peter also? Most Grants in Glengarry were United Empire Loyalists. There are five Peter Grants listed as being such.
In Names of Owners of Lots Given in McNiff's Map;
Dated 1st. November, 1786. Lake Township, Now Called Lancaster 1st Concession there is a Peter Grant on Lot 10. On the 1st Concession Charlottenburgh South Raisin River there is a Peter / John Lot 12 and a Peter Lot 18. In Petitions and Land Grants there are pages of petitions for a Peter Grant with one Peter Grant Shoemaker, son of the late Alexander Grant of W 1/2 Lot "D" S.S.R.R. Charlottenburgh, a UEL. There is also a Peter Grant formerly a Sgt. in KRRNY 2nd Bat. etc etc. In order to use this information we need to know Peter's father's name.

Tal