They have "trained" to be survivalists at home, although I would doubt it was very heavy training and likely to be keyed to video games and activities with friends. The father was pretty specific about that. So I think they decided to head to the farthest place they could get driving on a map. Perhaps Len Dyck had some RandMcNalley maps of Canada in his Rav4 or something like that.
I don't remember where the paved road ends on Route 290, but they went a substantial distance on dirt roads in variable degrees of repair to get to Gillam. I believe they knew they were not going to hook up with another superhighway to take them to the east coast of Canada. And I belive their journey beyond Split Lake to Gillam and the Bird area was deliberate, to live out their survivalist fantasy.
Maybe that was the intent but they got spooked and decided to hitchike out of town. I dunno.
Hoping they get captured and located today