Permanent force became Corps of Royal Canadian Engineers in 1903. Corps of Canadian Engineers was the militia arm, and according to Wikipedia, they didn't adopt the same badge as the regular force corps until the two components (militia and permanent force) were merged April 29, 1936.
Don't know about the GV cypher badge being worn by CEF engineers, but it would have had to have been limited to permanent force engineers if it was.
There is an entry on
Coulson Norman Mitchell on Wikipedia with a pic that shows him with the militia type badge. My guess from the sounds of it is that everyone who enlisted for WWI was, in effect, militia and not permanent force.