I have followed up on both of your excellent suggestions.
You may be interested to know that in the last few hours I think I have found William on the 1916 Canada Census of Manitoba, Saskatchewan, and Alberta. There is a Wm H Nixon recorded in the town of Gleichen, but at the time of the Census he was overseas on military service. This fits with what I know. The Census says that he immigrated to Canada in 1910 so that's a great lead for me to follow up. He was living as a boarder in the home of a Mr and Mrs Solberg in Seventh Ave.