Is solicitor-client privilege an absolute right to refuse disclosure?

When it comes to disclosure of a record subject to solicitor-client privilege, section 23 of the Act statutorily provides the government with the benefit of that privilege. The section does not create the privilege, but, by statute, gives to heads of government institutions the protection against disclosure afforded by the privilege by giving them, in an Act which promotes and favours disclosure of information, the discretionary power to refuse disclosure of such record. The use of the word "may" instead of "shall" makes the provision a permissive rather than a mandatory exemption. It means, a contrario, that the head of a government institution can disclose a record which contains information subject to solicitor-client privilege. I confess that the wording of section 23 now appears to me somewhat strange in view of the actual status of solicitor-client privilege, especially the "legal advice" privilege, which has become a substantive right to non-disclosure "as close to absolute as possible": see Pritchard v. Ontario (Human Rights Commission). However, at the time of enacting the provision in 1982, solicitor-client privilege was still more a rule of evidence relating to admissibility than a substantive right against disclosure. The concept of substantive right was still in its period of infancy and the privilege was far from enjoying the absolutism that it does nowadays. In any event, we are concerned here with a challenge to a refusal to disclose pursuant to section 23, not a challenge to a willingness to disclose.