There's something cool about Canada, I just found out that Alberta is the only large region of permanently inhabited human territory which lacks brown rats. One thing you have to remember is that the brown rat only began spreading within the last 1,000 years (in the process displacing the black rat), and it seems to have arrived in the British Isles only within the last two to three centuries. North America did not have the rat until Europeans arrived, and it didn't show up in Alberta until 1950. At that point the government attempted an eradication program. Apparently this can work because there aren't ecologically congenial corridors for the rats to constantly reappear through migration.
I used to work in rural Alberta, and it turns out that we could get the rat patrol out to our location faster than the paramedics.
Currently living, and having been born and raised in Alberta, I can confirm that this is true. In fact, there was an incident recently wherein a transport from another province was believed to have ferried a few of the pests into the city of Calgary and no sooner was one seen than the bylaw officers were on the beat.