Anybody know the story behind the non-standard fin marking (different flag)?
Gainsey, it's the old Canadian flag, which was a Red Ensign with the Canadian Coat of Arms. This flag was replaced by the Maple Leaf flag in 1965. Some older Canucks still think this was a retrograde move, but I like the very distinctive Maple Leaf. We don't get confused any more with
a British protectorate somewhere
like Bermuda or the Cayman Islands
For a good picture and all you ever wanted to know about Canadian flags, see
this Canadian Heritage site
And I've just noticed that you can see the old Canadian flag on MOTF's photo of the Old Warden Chipmunk on page 1 of this thread, which raises a question I've been wondering about. Why is a British T10 painted in Canadian colours? All the RCAF ones had bubble canopies and no undercarriage fairings and look quite different from the T10.
And finally, while seaching for a picture of an RCAF aircraft with a clear example of the flag (before I noticed MOTF's picture), I stumbled on the following picture, which, speaking as an occasional floatplane pilot, I think is the best example of formation flying I have ever seen:
Three RCAF Albatrosses in formation 