Air Canada requires documentation to be filed FROM YOUR PHYSICIAN DIRECTLY-- ours faxed the packet to them about 3 weeks prior to our flights.
Even so, the flight crew on our transatlantic flight was unaware of the allergy until we were over n. London and headed for the Scottish border-- when I told them.
I had mentioned it during check in, AND with the gate agent when pre-boarding. Oh, and obviously at reservation.
Basically-- mentioned it at EVERY opportunity, and each person was like "Wow! News to me!! uh... oh, yeah... wait..." It was maddening.