No idea if this will help but time and area make sense to me.
I have a James Millar in my tree. If you view the 1952 Census for Hillier Twp, Prince Edward County. There is a Las Millar lised.This is actually James.I am a descendant of J.B. Millar Jr. trying to prove the link between this line and one that I have found in Quebec.My challenge has been in locating additional info on all siblings listed.I suspect that the J.B. Millar Sr. and Catherine are the ones listed in mariage records for St. Raphaels, ON and the family was on a slow migration Eastward but most of them disapear by 1871 and may have returned to Quebec.
A mariage record for any of the siblings listed in the census above may give me the Catherine's maiden name.
If you have a marriage record for James that indicates Caherine's maiden name as Clairemont, I have additional info and I'd be very interested to hear from you.