Archie and Margaret were not married by the time of the 1851/52 census. Margaret's death record in 1893 indicates she was born about 1831 in Whitby, Ontario, and that she was Presbyterian.
Whitby, Ontario Co., Canada West
Harnden, Luther, miller, b. USA, no church, aged 69, married
Harnden, Sarah A., b. USA, aged 59, married
Harnden, Margaret A., b. U.C., aged 20
Harnden, Samuel, miller, b. UC, aged 22
Harnden, John, miller, b. UC, aged 19
Ferguson, Betsy, servant, b. UC, no church, aged 15
Luther Harnden, d. 24 May 1876, aged 93 years, gentleman, b. State of New York, cause: old age and decay; no physician present at death; informant: Reuben Harnden of East Whitby, son of deceased, Episcopal Methodist.