Or the Governor could just expunge MJ convictions across the board.

That would be a. easier b. effective c. cheaper.

And order all credit and employment DBs in the US and Canada to remove such entries.

Unfortunately, the employers could find any number of reasons why else not to hire the applicant, once they know the applicant is an ex-felon. Just as they can find any number of reasons to fire employees in protected classes (age, etc.). Something stronger is needed, but if Columbia's good lawyers don't know what it is, I certainly don't.