what is the parraell of us american border

The parallel of the U.S. and Canadian border is the 49th parallel north. Most of the Canada–U.S. boundary follows that line, from British Columbia across to Manitoba, though some parts deviate from it.

Quick note

If you meant the U.S.-Mexico border, that border is not called a parallel; it follows a mix of rivers, surveyed lines, and artificial markers instead.

In simple terms

• Canada–U.S. border: mostly the 49th parallel north.

• U.S.–Mexico border: not a single parallel.

The phrase people usually want here is “49th parallel.”