There's a concierge in DUB these days (or at least was in January). Suggest showing up with plenty of time before bag drop cutoff and asking for Concierge help if they won't short check the bag to YYZ for you. As yyzgigi says, just say you need access to it in YYZ and will be going landside before your onward connection ("to meet my family member and give them a gift that's in my checked luggage and is 750ml of liquid so can't be brought on board").