I called and they said the USA/Canada map could not be put on the 50m. I'll try calling again, see if a different rep knows what works.
I also called and said I made frequent trips to Canada, and that I really needed that in a GPS. At first the rep said I could return it and get the 55. I told him I would just return it. I asked him if he was sure there was nothing he could do. Then he said we could put North America on and he guided me thru the process.