Cracked it!

Patience, perseverance, and not believing what we've been told - or at least interpreting it less literally, given that the Sth side of the St Lawrence river would have been/is rather close to St Lawrence County in New York State.
Adam Brown RICHARDSON's census data all indicated he was born in New York around 1835.
The recent flurry of activity trying to connect him to the Bermuda RICHARDSON family that turned out to be that of James and Margaret (MABON) RICHARDSON was inconclusive, but there is a growing body of circumstantial evidence of a connection - my theory being that James remarried, to Christian OUTERSON.
Who has finally been found to be Adam's mother.
A very big thank you to those behind the indexes on the Huntingdon County and the Seigniories of Chateauguay and Beauharnois website.
I was actually looking for anything that provided evidence for the age of James, Christian's husband, that may add even more fuel to my theory of this being his second marriage, and had turned my attention to Quebec, given that their son Robert's bio stated that he had emigrated at age 6 to Quebec, and taken part in the Patriot War of Canada at aged 16-17.
Still pinning my hopes on a heads of household census of 1841 for Chateauguay, but as there's also a James shown as being buried in 1840, I'm not holding my breath.