I have found a pretty big clue on the Island connection,from Sligo to Canada. The death certificate of Catherine Buchanan in Chicago, IL 5 Sept 1906 lists her parents as Catherine Knox and John Island. Related searching yields that Catherine Island was born in Ballymote Co. Sligo, 21 June 1827. Around 1850 she went to Canada and she married James Buchanan (not sure which happened first).They had eight children, six of whom were still living in 1900. In 1890 James and Catherine went to Chicago where several of their grown children were living.
At the same time, a woman named Fanny Island married George Buchanan, who also had a family in Canada. I am guessing these are a sister and brother of Catherine and James respectively. Does anyone have info to add to this puzzle so we may finally get to the bottom of the Irish origins of the Canadian Islands?