Question

the border between canada and the united states is a thick black line?

Answer 1

Well there's no actual line going along the boarder unless you're talking about maps lol

Answer 2

Usually with maps it's a simple line to indicate countries, as well as states.

http://images.nationmaster.com/images/motw/americas/canada_pol_94.jpg
map image ~ with a black line

Answer 3

Yes, it would. The line represents separation between 2 countries.