I think Transport Canada has bigger fish to fry than to worry about the size of your letters. There are some funny rules regarding letter size in Canada and you can get special permission to use smaller letters if there is not enough room on the side of the plane. Then there is the issue of is it a Certified aircraft or an Ultralight (Canada's version of Light Sport). I think worry about your rules and if you fly north of the 49th you probably won't be bothered.
No guarantees just my thoughts.
Norm