I have just seen on another site that there is Passport Control in DUB Transfers/flight connections and arriving from YYZ you will clear Irish immigration there (EU), which then of course gives you open access to fly from DUB-NQY which has ''no border'' as such > aka 'Common Travel Area'
As for your luggage if you hang onto it until Toronto YYZ then ask there to check it through to NQY and you may get a result.
Ask them also if they can issue your DUB-NQY boarding cards as well.
In 2012 Air Canada and Aer Lingus Signs Interline Agreement and is pleased to interline with Aer Lingus as it will complement our Toronto-Dublin seasonal service to make it easy to fly year-round between Canada and Ireland via convenient connections through to London Heathrow Airport, and UK regional airports from Air Canada's largest international station YYZ. We intend to follow through with other measures, including a full code share relationship with Aer Lingus.
It seems-
No PLF or Covid Tests needed to enter Eire.
UK GOV says no PLF needed if flying in from Eire.