B-1, r. 3.1 - Code of Professional Conduct of Lawyers

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88. A lawyer must not act in a matter against a former client of another lawyer in the same firm if, when the other lawyer acted for the former client, he obtained confidential information relevant to this matter and the disclosure thereof could prejudice the former client in this matter.
However, a lawyer from the same firm may act in this matter if the former client consents or if doing so is in the interests of justice, having regard to the following factors, in particular:
(1)  the measures taken to ensure that no confidential information obtained by the former lawyer will be disclosed to him;
(2)  the extent of the prejudice caused to one of the parties;
(3)  the good faith of the parties;
(4)  the availability of another lawyer with the requisite competence; and
(5)  any other issue of public interest.
For the purpose of applying the second paragraph, the lawyers from the same firm must not, except where the former client consents, discuss the matter between themselves, and the lawyer of the former client must not participate in any manner in the performance of the other lawyer’s mandate, discuss it with another person in the firm or disclose information concerning the former client.
O.C. 129-2015, s. 88.