thats not actually all that true, spread usually tends to respect borders a little bit, but only because those borders are generally a choke point. Usually spread is going to be via things like planes and airports, which tend to uh, bypass them. Although i wonder how much livestock flies by plane.

It also depends on how it spreads, there are a few theories, one is due to the migratory behavior of birds, and if that goes over canada, that could very well be the case, but it’s not strictly clear how it’s even managing to spread right now.