Upvote:7
When you leave the United States, you are not generally subject to inspection by a US immigration officer. Rather, the US will know that you have left (and the date) because the airline will transmit a list of passengers leaving a country to the US government. So they will not stop you from leaving, but they will likely know that you have overstayed because of this information coming from the airline. This will likely make it difficult to enter the US in the future. (How difficult depends on various factors, in particular exactly how long you overstayed.)
As for Canadian immigration, you will see them only when you arrive Canada, and whether or not you overstayed in the US is not their concern.
Upvote:12
There are no exit immigration checks in airports in the US:
Canada doesn't care how long you were away.