Specifically - there isn't an excise tax here in Canada on soda (pop) particularly from the US (NAFTA, and whatever you want to call the next version of it). Possibly, and only possibly, they've issued an edict from the CRA (the IRS equivalent) that says you have to pay HST on consumed beverages on the ground. That HST would be recoverable as a business expense though (Delta would simply have to claim it on their HST return as an input tax credit). That suggests perhaps that they just don't know how to account for it or don't want to do the additional paperwork. That seems like something they could negotiate if they want to. Further, I have received PDB departing Canada on United, Air Canada and American (I do not fly Delta often - they are great but don't go where I need to quite as conveniently) . That doesn't explain your trip TO Canada though - that makes no sense. I think the flight attendant was tired that day.