In Canada, after you fill out your ballot in secret, you fold it up and hand it to the poll worker, who tears off a stub and then hands the ballot back to you,

In Canada, after you fill out your ballot in secret, you fold it up and hand it to the poll worker, who tears off a stub and then hands the ballot back to you, and then you insert it into the ballot box yourself in plain view. I don't know if this is the current case (or perhaps your scenario is one of the reasons for the current procedure), but they can just put a serial number on the stub so that the poll worker can verify that the ballot that was handed out was the one just filled out.