I suspect that it also had to do with the simple economics of demand and distribution channels. A lot of the off-brand machines in the US were placed by local and regional soda manufacturers. Often times, in gas stations and corner stores. With many more population centers in the US than Canada, there were a lot more opportunities for the soda companies and therefore a lot more machines placed in stores and other venues. That's my uneducated guess anyway!
While the variety of the machines in Canada may be limited, one of my favorites in my collection is a Kelvinator FE-51 that was originally in a general store on Pelee Island in the middle of Lake Erie! I can't wait to get it completely refinished but it looks good as is. The chrome trim was something not seen on many US machines.
Tim