My friend is transiting through YYZ, so he will be in the domestic area until he is ready to walk over to the E gates. It is clear that he has no access to the MLL on arrival as a E35, that's why I asked if he has access to the domestic MLL for showing his departing YYZ-LHR boarding pass. AC website did not state clearly that access to the domestic MLL requires a domestic departing AC flight.

I will pass on what hydrogen said, but obviously subject to lounge agent interpretation.