Unfortunately, the Dr. John McArthur Dunsmore to whom you refer was the son of the Dr. John McArthur Dunsmore to whom I referred by his first marriage. The Dunsmores I am trying to trace arise from his second marriage to Edith Gould Halford(by the way, I thought the first wife was named Julia Campbell).
I really have nothing on the children of the first marriage - I only found out about the Dunsmore family connection 3 months ago - and not a lot on the children of the second. As a result, I really can't help you
Interestingly, yesterday, I received an E-mail from a Dunsmore now resident in London who comes from Alberta. It is possible he descends from your Dr. J. McA. D. - I am going to ask, and will contact you if I get anything