The US / Canadian border in the West is interesting. It seems between west of the great lakes and east of Seattle there isn't much connection across the border.
I really wanted to look at the map in the context of where actual countries were so I threw together a Google Maps overlay. I couldn't believe how accurately the connections followed country lines, it was amazing!
It is a lot easier to move around and work on one side of the border or the other, which leads to people naturally not meeting people on the other side.
In the east there are so many more people and there is so much cross border traffic due to trade (particularly from the auto industry) that a lot more cross border connections exist.
I've been to the Eastern part of the border: Stanstead, Quebec/Vermont. Over there, some of the buildings are right on the border. One of the guys I worked with lived in apartments which had their parking lot technically in the US.
On the other hand, if you were to think of the kind of people in each country who wouldn't have any friends at all in the other country, wouldn't they probably live around there?
The US / Canadian border in the West is interesting. It seems between west of the great lakes and east of Seattle there isn't much connection across the border.