Just to say thank you to all those who contributed to the thread and a quick confirmation that I had no problem whatsoever getting into the domestic MLL at YUL in-between two Y flights in the morning with the boarding pass for an international departure in the evening.

As for access to the international MLL at YUL, I was surprised about the "segregation" of the domestic from the international area. As it is no actual barrier with passport control, but only some folks standing there with handheld scanning devices refusing domestic pax to stroll any further, I had some difficulty understanding the rationale of the set-up. Is it just for keeping domestic passengers away from the duty free shops although they cannot purchase anything without a boarding pass for an international depature anyway? That would be appear a somewhat drastic measure as all the other tenants in that area would probably be more than happy to welcome more customers purchasing food etc.(or is that tax free as well?)