I am also looking for St-Onge's from Beauharnois and Valleyfield. It seems there is little to no info on the net about St-Onge's from Beauharnois.
Mine are Andre St-Onge and Angelique Lanoix/Lanoy; and Antoine St-Onge and Catherine LeBoeuf. Catherine is the daughter of Charles LeBoeuf and Francoise Cuillerrier (Spooner). Catherine had a first marriage to a man possibly named Chaloux, as her son, my uncle, gave his mother's name as "Mary Charlois" on his marriage license and I found in the 1865 census that it was her second marriage. She came from Valleyfiled and would have married there I would presume.
All moved to St. Lawrence County NY about 1840; lived in Gouverneur, Lisbon and Ogdensburg.
Antoine and Catherine are my gggg grandparents; I believe Andre is his brother but no proof yet. Antoine named a son Andrew, and both men are the only two of the St-Onge line who moved to the NY and changed their surname to "Santaus". The only living Santaus' now, hailing from Meriden, CT, and spread around the US, are the descendants of Andre and Angelique via their son Jean Baptiste and his wife Sophia Laurent (Rollins).