Huh? I think you're fooling yourself.

So on Friday BMO closed at $95.22 on the TSX and $US 73.44 on the NASDAQ - which reflects the forex differential ($CAD worth $0.7712US on Friday)

For the sake of simplicity let's suppose that the Canadian $ jumped to par and BMO's stock price remained at $95.22 on the TSX. It would jump to $95.22 +/- a penny or so on the NASDAQ to reflect the new exchange rate. But you haven't made any money. The $US95.22 is now worth $CAD 95.22 - which is the same as the $US 73.44 was worth previously.

Think it through - you really are kidding yourself.