Hi Alex;
Hopefully, you'll be able to obtain the info through this forum; however, if not, I would recommend checking out the Canadian Council of Archives - Ottawa, Ontario
info@archivescanada.ca.
I found them extremely helpful in obtaining detailed military information concerning my great uncle (1914-1919).
Also, the county museums can be a good source of information. Since Flying Officer Barr is from Hamilton that would place him in Wentworth County.
In searching my great uncle's war record, the serial or registration number that is assigned to enlistees when they are enrolled into the military can set you on the "fast track" for obtaining information. Good luck with your search.