Fellow researcher Marika Pirie (mentioned below) alerted me to this fantastic Library and Archive of Canada website where you can search for those who fought in WW1.
Marika alerted me to one particular soldier:
Born in Punjab in January 1883, Waryam Singh was a labourer who joined the 38th Battalion of the Canadian Overseas Expeditionary Force in Ottawa in May 1915.
Being in his 30's, what he did to get to Canada would be interesting to find out!
While the first two pages of the Attestation soldiers undertook is now online, more details will be released on the site later this year about each soldier. It'll be interesting to find out more about Waryam Singh.
Update: click here for an interesting article about another Canadian Sikh who served.