It took a bit of searching but I found the info on where John Blair Montgomery died.
www.collectionscanada.gc.ca/databases/index-e.htmlWar Diaries of the First World War
under search topic try
MD No 11 Victoria
If that doesn't work, put in only Victoria
The information that you want is on October 1918, page 22
I will post the info here just in case you can't bring it up as it was being obstinate tonight.
23/10/1918 12:30pm
No 2020874, Pte Montgomery, J. died of Influenza and pneumonia
I suspected that if he died in Victoria it would have been from influenza but had to source it. I found this info by looking at Nursing Sister Marjorie Beatrice Moberley who wasn't included in the CWGC and there was a forum that was trying to source info to get her included.
I'm not sure if this site will work or not but will post anyway
http://1914-1918.invisionzone.com/forums/index.php?showtopicFrom the Royal BC Museum archives
John Montgomery
age 29, died 1918/10/23, Esquimalt (this is the military base in Victoria, BC)
Registration # 1918-09-038195
Margaret Montgomery
age 40, died 1905/11/13, Vancouver, BC
Registration # 1905-09-121335