Thanks, Donna. I have tried to find more about Bill Barber but have had no luck. He could be any of the William Barber's that lived in Toronto at the same time as Donald. They look too young in the photo to have been WW1 army buddies so figure they must have grown up together or, at least, have been high school friends.
I don't know how much info you have on your Bill Barbers but here's some on Donald Gibson that may jive with that info.
1. Donald Gibson, born 1891, Toronto, to William and Josephine. 12 McMillan Street.
2. 1901 census, East York, 31 Birch Avenue
3. 1911 census 31 Birch Avenue
4. 1914 Married Emma Hosmer
5. 1916 Lived at 116 Birch Avenue.
6. 1916 Died in WW1.

Maybe I will try to have a further look into some of the Bill Barbers, I like mysteries!!