As far as I'm aware, the placement of the spare wheel on the front panel and the use of a Motley mount for the Bren on the SWD Big 4 were pretty much only Canadian practice. I'm sure that Lex will confirm though.
This picture appears in "The Canadian Military Motorcycle" by the late Clive M Law, who stated they are from a Reconnaissance Squadron of the 2nd Canadian Division on 18th November 1940 in England.