Take a look at Google maps, streetview. Just a couple of miles east of Blaine, you can follow the road that is the border. A house or small apartment building on the US side, a two-lane paved road, then a house on the Canadian side of the road. No fencing other than the usual property fences you would find anywhere.

All along the border, they have put up jersey barriers on a lot of the country roads that used to slice through the line. But, in many places, there are houses on both sides of the road.

Here's a good example in Vermont. Vermont is on the south side of the street - note the house with the Bernie Sanders sign in the front yard. Across the street is a house for sale, in French, on the Quebec side.

https://www.google.com/maps/@45.0058...7i13312!8i6656