What is the legal test for disclosing privileged information to a former client in a disqualification proceeding?

The first issue is whether the transferring lawyer is in possession of confidential information. In disqualification proceedings the former client bears the initial burden of showing that the retainer under which the confidential information was acquired is sufficiently related to the current matter. If that threshold is met, there is an inference that confidential information was communicated and also that its disclosure would prejudice the interests of the former client. The burden then shifts to the transferring lawyer to rebut the inference, but without revealing the specifics of the privileged communication. In MacDonald Estate v. Martin, Justice Sopinka labelled this a "difficult" burden to discharge.