I had not realized that there was anywhere in North America that was "rat free". Would love to make Sunnyvale rat free but with all the old orchards and what not I doubt that is feasible.
Part of the reason that they can be controlled in Alberta is that they can't survive the winter outside of human structures. Combined with the fact that the border areas are relatively sparsely populated farmland, it is more a case of eradicating small isolated populations than controlling rats en masse. The rats can do a bit of "island hopping" in the summers, so an active campaign has to be maintained to keep them out.
The other reason that it is possible to maintain, of course, is the fact that the decision was made BEFORE rats invaded.
I live in Edmonton, Alberta. In the last 10 years the only rats I've seen are the ones used in the neuroscience labs at the University of Alberta.
In truth, my house got a infestation of the smaller deer mouse [1], 2 years ago. But they are indigenous to Alberta and much smaller and easier to catch than the brown rat. It was quite easy to get rid of them, a cleaning in the garage and some traps did it.
I lived there for decades and never saw a rat. I guarantee they have rat infestations occasionally, but they are caught and eradicated pretty quickly. I know they had one down near Lethbridge recently, but I think it turned out to be pet rats that were let loose and started breeding.
