Chances are that if the situation is bad enough in the US to flee the borders will be shut down and heavily patrolled and crossing them will be quite difficult. In theory I could easily canoe across the border from Minnesota to Canada. However, if that ever becomes something I would attempt, there is a very likely chance border patrols would catch me. I think realistically the only way to get out of a country with a family is before the shtf. It would be much easier to do this on an individual basis than with a family of four, two of which are not yet teenagers. There are plenty of places I could simply walk across the border from Minnesota to Canada, but again I'd have to be able to avoid getting caught and my kids would have to be able to hike a very long way. As a practical matter fleeing is a lot harder to pull off than it seems.