I'm not sure we could prevent them from joining if we wanted too
Per the U.S. Article of Confederation
XI. Canada acceding to this confederation, and adjoining in the measures of the United States, shall be admitted into, and entitled to all the advantages of this Union; but no other colony shall be admitted into the same, unless such admission be agreed to by nine States.
I not sure the Articles of Confederation were ever formally repeal, the Constitution just superseded it
Here is our out. Canada is no longer a colony. It is now a fully independent member of the British Commonwealth.
Nice find, Top