In my making modern America history class, my professor talked of after the civil war, congress debated asking Britain to hand Canada over to the United States. If this is true, why did they debate this, how close were they to doing it, and what was the British response?
That's a new one!
Could your professor have been thinking of Article XI of The Articles of Confederation, which reads:
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.