The Customline had a side trim that went all the way to the front where the Mainline did not. Mainline cars started out as trimless early in 1956 production but changed to the abbreviated side trim at the rear and added trim around front and rear glass. There were other interior trim differences and exterior options but the external side trim differences do stand out enough to tell the tale.
I can't say if there were differences in Canadian production or not. This link is a good one,
https://1956-ford.com/1956-ford-cars-all-brochure.html