There does not seem to be any US airport (or any other US port of exit) where Canadian authorities enforce any kind of preclearance. The page of Public Safety Canada that describes the process does not mention any current enforcement of this preclearance by Canadian authorities.
However, the currently active agreement allows Canada to do so:
It enables Canada and the U.S. to expand preclearance for travellers at land, rail and marine facilities in both countries, as well as at additional airports.
While there doesn't seem to be any Canadian preclearance enforced at the moment, there might be some at the future, without anything precise disclosed by the authorities:
“Canada is committed to expanding preclearance and we continue to examine possibilities for expanding preclearance operations to new locations across our country and in the U.S.”
– The Honourable Bill Blair, Minister of Border Security and Organized Crime Reduction