Aer Lingus and Canada
Aer Lingus can fly to Canada and has done so in the past but that was from Dublin. The possible issue here is an Irish airline picking up passengers from a foreign country (the UK as Northern Ireland is part of the UK) and taking them to another foreign country (in this scenario Canada). The so called Open Skies arrangement between the EU and the USA allows for this (which is why Air France ran a Heathrow - US service) and of course within Europe is has been common for many years - EI running Manchester-Copenhagen many years ago being but one example but I do not think this applies to Canada