Is he aware of the new rules? It might the case that he simply is unaware of changes to import regulations in the UK that came into force only a week ago.You picked the wrong example, the Canadian postie won’t say boo, that l can confirm.
At the end of the day it's not actually designed for the ease of foreign postal or courier services (other than they presumably don't want to be stuck with an undeliverable package or package that is held up in customs) but to assist the recipient in getting their goods. If you send a package the courier at your end may well accept it without an EORI number for the recipient, but it could still get held up at UK customs.
If you are sending stuff to the UK on a regular basis you perhaps should ascertain the EORI number of the consignee and let the Canadian postman know about it, for your own convenience.