The vast majority of the US/Canadian border is unguarded and there are hundreds of roads the guy could have alternately taken.
Any sophisticated attacker would realize this and simply go a few miles out of the way to one of those logging roads.
I hardly think that your example offers evidence that border security enhances national security, only that it did in one isolated instance (with a very stupid terrorist).
Odds are if the terrorist failed to realize he could cross the border without being screened, he would have made some other mistake that would have foiled whatever his planned attack was.
