These docs indicate a 2 minute separation should be given when
departing behind a Boeing 757.
ASA87 I couldn't find this in either of the docs you mentioned - as far as I can see there is only a rule regarding 757 separation on approach.
I'm interested in this topic - our Ops manuals are basically worded as per AIC 17/99 (Pink 188) and no one has so far shown me a reference for a departure rule regarding 757 v a following M category, though there seems to be a wealth of anecdotal evidence supporting the "2min rule".
I'd appreciate any official references.