just like the Ruger 556 both of these really doesn't bring anything new to the table, while ther are few people in Canada that will buy it based on brand loyalty, there just won't be enough sales for a dealer to spend the effort and resources to get the manufacturer to make a US export complient model and bring it in. Perhaps once they establish themselves in the US market, the manufacturer might move towards a Canadian version.
There are lot of quality AR's to pick from in Canada, like PWS, LMT, KAC and HK that is lot more refinement than the Sig or you really have your heart set on a piston AR than PWS, Stag and HK are all available as well, but if you are buying it for the brand name than spent money or do the paperwork yourself to export it on your own.