Per CARS,
With two pilots, 14 hours is the limit.
15 hours if there is an augment pilot in the jump seat.
17 hours if the augment pilot gets a seat in the cabin.
20 hours if the augment pilot gets a bunk.

Duty days can be extended up to three extra hours for unforeseen circumstances.

Union rules may be more restrictive.
As far as I know, f/a's don't have CARS duty day rules. Only union rules.

There have been flights that have left Europe several hours late, did a tech stop in the Maritimes to swap crews, prior to continuing to Central Canada.
Same for flights leaving Asia late. Tech stops in YVR for crew changes.