First of all, we don't have an offence for simply being a member of a criminal organization even where that issue is not in doubt. Rather, the offences are for participating in the activities of a criminal organization with a view to enhancing their capacity to facilitate or commit crime, for committing an offence for the benefit of, the direction of, or in association with a criminal organization, or for instructing somebody to commit an offence for a criminal organization. A membership offence per se is what we call a status offence, and it would certainly raise pretty significant charter issues, freedom of association being one of them.
On a reversal of onus, there are some reverse onus provisions dealing with particular issues in the Criminal Code, but they are pretty restricted. One of the initial questions will be, exactly what is a member? What are the characteristics of membership in a criminal organization? In some cases, the Hells Angels, for instance, for the full-patch members who wear the symbol, that may be fairly clear, but in other cases with street gangs it's going to be almost impossible.
Assuming that you could establish what membership meant, if the offence depended upon that allegation, and you simply reversed the onus, then it would be difficult to see that this would survive under some of the more basic guarantees of the charter.