Originally Posted by The Lev

When travelling to the US via YYZ, there is a connections option that lets you bypass Canadian customs and go directly to US customs. Problem is that I don't think there is anywhere along the line where you can go for a smoke.

You will need to clear Canadian customs, go outside then go back in and clear US Customs (you do this in Canada rater than upon arrival in the US). Give yourself at least an hour to get through US customs and security - with 2 hours 40 minutes you will have plenty of time unless your flight is delayed.