There are plenty of reasonable scenarios where a Canadian might want a shoulder holster. First to mind comes Timber Cruisers, Trappers, Tree Markers, and Prospectors with ATC. Also, Canadians participating in handgun hunting in the USA or other countries that permit it (Safari). It is possible they might have an occupation where they carry concealed out of country. This list is not intended to be all inclusive, but a mere starter.
I myself followed this thread as I am looking for a good shoulder holster for handgun hunting I do in the USA.