"Alberta has no rats" is a bit of a simplification, as the linked article goes into in depth. They do find rat investations (typically) in the border zones, and some sneak through, both wild and domesticated. Due to ongoing management though the statement is true in broad strokes. We have lots of mice and all sorts of ground squirrels (including a ridiculously awesome "museum") but thankfully very few rats.
Canada's shipping ports have had rat infestations for hundreds of years, even up the Great Lakes. DNA studies show that once a local population became established long ago, it defended itself repeatedly from incursions, and carries on. Alberta has no sea ports, so rats hitch rides there on trains, trucks, and in packaging. The scale is much, much smaller, so Alberta is somewhat able to eradicate them.
The exterminator told me you either have rats or mice. That's 'cuz the rats are good at eating the mice.
In some parts of the world I bet that's true. I can say with a high degree of certainty that I have neither.