For example leaving the Schengen area it's obligatory to go through "exit immigration" and get your passport stamped. Leaving the US, you show your passport to the airline, but usually there is no formal immigration check at all.
- Arrive in Pearson
- go to passport control, scan passport at kiosk, kiosk spits out receipt
- you flash receipt to a border officer at the stairs out of passport control
- go to baggage claim
- get bags
- go to customs
- hand passport with receipt to officer at customs
- welcome to Canada
I haven't had that experience when leaving other countries bound for the US; like GP said, I've had to show my passport to the airline to board, but I believe that's to fulfill the requirement that they made good-faith effort to ensure I'm capable of entering the US.
I have not ever heard of that happening, but if I did hear about it happening to normal people (i.e. people without a criminal warrant) I would probably stop going to the US.
Driving across the border from the US back to Canada you don't talk to US border agents.
Flying from the US back to Canada you don't talk to US border agents.
There are massive data sharing agreements between US and Canada customs. US and Canadian sides can pull full criminal records, and a pardon means nothing. Exit data is shared in both directions as well.
EDIT: I do remember hearing some cases of being searched when leaving through land borders, but that's more of cars being searched for smuggling IIRC?