I'm guessing it would be America, which is less of a problem because statistically most Redditors are American, and the two countries are diplomatically and socially very close, so a large number of Americans visiting a sub about small Canadian towns is less surprising than large amounts of Russians.

It'd be like if /r/queenstown had Australia as its second-biggest country of origin. Aus and NZ are so closely related (not just geographically, but socioculturally) that you'd expect that to be true, especially given Australia's comparatively large overall population compared to other potential candidates (per capita, you might not be surprised if a country like Tonga or Fiji were even higher, but in absolute terms that would be very surprising).