Don't know how much I can safely give up without threatening my own identity, if anything.
How I know about it: I have a temporary placement with policy integration and my supervisor is a high level manager. We talk and he sometimes tells me things he knows he probably shouldn't, that he thinks he can trust me with. What I am writing next is everything I know about it.
In Canada right now, feds (I don't know which branch they work for but it is within the policy integration department) are meeting and discussing the proposal of a bill that would essentially give police the power to do general surveillance of red mail boxes, and those who use this service. Within the meeting, dark net markets were specifically mentioned as one of the issues the bill proposal would help address.
I thought it might be important to open up discussions about this.
Despite being utterly unfamiliar with the difference between privacy rulings regarding mail between other countries and Canada, it does seem to me this isn't yet a genuine cause for concern.
Based on your description, it sounds as if at this stage it is little more than someone in some agency is wanting to introduce legislation (which then needs to follow political procedure for adopting) of the police are allowed to sit and watch general mail activity at these boxes.
It doesn't appear to be saying that mail placed in red boxes is open to search; only that they can keep an eye out for suspicious activity. Legislation such as this does exist in other places, most notably in the USA, where the police absolutely are allowed to sit and observe people sending mail and pass along concerns to the postmaster.