When you read the letter to Robert and Ruth you should note that 1)Alexander was Margaret Scott's first husband not John.
He is listed in all announcements as Alexander. His father's name was John according to the family tree The McDonalds of Arnprior.
2)She remarried Samuel McDonald/McDonnell who was a blacksmith.They lived on lot 4 on Daniel St. in Arnprior. They are listed in the 1851 and 1861 Cencus.
His son Duncan married Julia Keyes. They were the parents of Mary Henrietta who marrried Maurice Jeremiah Buckley. Olive Carmen Mcdonald and James K. McDonald who married a Miss Lafferty.