anneelaine, don't be relying on your Canadian acquaintance's opinion about the uniform.
As we have seen, it is hard even for people in the know to distinguish WWI uniforms.
The one in the photo would probably look to him like a Canadian uniform ... because it does.

And because Canadian uniforms are the ones that he would have seen before.
If he were to see a British uniform from WWI, he probably would not be able to tell them apart either.
If your fellow had been in the Canadian military, he would show up in the CEF attestation papers database. (We did not suffer losses of those records the way England did in WWII.)
If he really wasn't going by his real name, I don't know that we stand a chance! And the whole thing just becomes more confusing ...
For names that someone might not have liked, born around the right time, the only one I see is Enos Staveley. There were a few of them, in what seems to be a bit of a long line of Enos-s, and it's a little confusing - all in Lancashire. One was born in 1896 in Chorley reg dist and seems to have married in 1925 and died in 1945 in Haslingden reg dist. In 1911 he was an engraver's labourer, son of an engraver, so not especially posh.
Maybe we'll have to reconsider one of my musical Staveleys from way back ...
WWI medal cards are a good way to tell whether someone was in the military, even if their records did not survive. The Staveleys in the list include several Charles-s, that Enos, and the odd other odd name, like Elijah, and also a lot with just initials.
I dunno, what with the snooty attitude and giving your gran (that's Annie, the mother of his daughter?) a grammar book for Christmas, the "violin maker" story is starting to sound more plausible.

(My grandfather the son of the musician was certainly snooty when he married my grandmother; he made her change her given name because hers was too "common" for him.)
Let's hope that the person you are trying to contact who is descended from the Charles who had been settled on will respond and know about that Charles, or put you in touch with an older family member who would.