Could it be...?
I've seen pictures of the flag that preceded the lovely Maple Leaf, adopted in 1965. It's called the Canadian Red Ensign. It has the Union Jack in the upper left corner, where the blue field with white stars is on the US flag.
A tiny picture, as would appear on currency, of a flag with a cut-out in the upper left corner might be mistaken for a US flag by people (like Americans) predisposed to see a US flag, especially if the viewer wasn't acquainted with Canadian history.
Were there $2.00 Canadian bills before 1965?