Before you go through the expense of an investigator, I'd try the University of Saskatchewan's archive. they hold the files for the SLI.
http://www.usask.ca/archives/sli/
A quick search on SMith's name pulled up all sorts of available records!?
http://www.usask.ca/archives/sli/sea...sortorder=name
Looks to be info from Part I orders... there is also another Lt. Smith listed too. They may be related. It looks like an archivist at the UofS might be able to give you more clues to Lt. Smith's relatives including wartime and postwar addresses. His is a very common name, but if you know the hometown he may be easier to track.
If he was married. His wife's family may have a more uncommon name to trace. My experience in tracking down vets and their families from the prairies has been quite fruitful and IF he is from Saskatchewan I think it is likely that the family (in some form) still resides there.
Good luck.
Bill.