What is the legal test for obtaining confidential information from a former client?

With respect to question number (2), and this in my opinion becomes relevant only if question number (1) is answered in the affirmative, Sopinka, J., at p. 725 of MacDonald Estate v. Martin stated: "The second question is whether the confidential information will be misused. A lawyer who has relevant confidential information cannot act against his client or former client. In such a case the disqualification is automatic. No assurances or undertakings not to use the information will avail. The lawyer cannot compartmentalize his or her mind so as to screen out what has been gleaned from the client and what was acquired elsewhere. Furthermore, there would be a danger that the lawyer would avoid use of information acquired legitimately because it might be perceived to have come from the client. This would prevent the lawyer from adequately representing the new client. ..."