Guy Powers is an agent with Canadian Intelligence.
That is an assumption. We know he is Canadian because of who is publishing the stories and because it is mentioned in the first adventure that planes were being shipped from his homeland over to England for the war effort. The Intelligence part of the statement, though, is a guess since no department employer is ever mentioned but he is dubbed a "secret agent" and he is often summoned by people who are simple needing his kind of help.
The whole "secret agent" when everyone knows who you are ("Powers, I need ..." or "Mister Guy!", or a late night call by the police for help) is questionable. Still, since he is the one called and he is the one coming up with the answers, "agent" definitely fits. The "secret" part, not so much.
Powers definitely dresses the part with a trench coat and a hat. He sports a pencil-thin mustache and when his head is not covered, his hair is shown to be dark and wavy. He is not adverse to mixing it up with bad guys with either a fist or a gun but he also uses his eyes to observe and his brain to reason which is refreshing. Interestingly, the way that he is depicted sometimes makes him out to be a very handsome, dashing individual and at other times he comes across as a stereotypical villain!
The first few cases we find Powers working are all in the pursuit of enemy spies and saboteurs, German mostly but he keeps an eye out to the Far East as well. As time goes along and WWII draws to an end, he is found in an office bearing the title "Guy Powers Investigator" taking normal clients in his obvious role as a private eye, though one of those cases will take him over to Africa which he does without batting an eye.