A quick search of the Attestation Papers online show six James Vickerys that served in WWI.
Here is the link to the search, if you look at the attestation papers you may be able to figure out which one is your Grandfather by identifying NOK, place of residence, etc.
http://data4.collectionscanada.ca/ne...e.html&r=0&f=S
Soldiers of the First World War
Regards,
Jeff