Hi Mel - I really wish I could help you with your McDougalls but at this point I know very little about my McDougall ancestors prior to the time they appeared in Ontario, Canada. I do not know the names of either Alexander's or Leah's parents nor have I been able to discovered where Alexander was from. It is only through information from family members that places Leah Armour's origins in County Antrim, I have not found sources to support it. In case any of what I have will help you, I've included the little bit of information I've found below.
Alexander McDougall (c1808-1860) married Leah Armour (c1818-1900) in Ireland (date of marriage unknown, probably sometime before 1839, location is speculation). Leah was probably born in County Antrim, Ireland. They came to Canada about 1842 with their eldest child Eliza Jane (born c1839 possibly at Ballymena, Ireland). Eliza was 3 years old when they left Londonerry, Ireland to come to Canada. Their second child, Caroline is said to have been born in Montreal en route to Renfrew County (census indicates she was born in Quebec). Alexander McDougall located at Lot 18 Con 6 in Admaston Township, Renfrew County. May have come to join John McDougall (maybe a brother) who had come to Canada about 1820 to settle in Lanark County. John McDougall was married to Sarah Campbell and they moved to Admaston Township about 1840 locating Lot 19 Con 6. John died c1855. Sarah and Alexander McDougall both ran hotels on the Admaston Road on their respective lots.