I think it's the Supreme Court Act, which lists the eligibility requirements for the Supreme Court. It may be the Judges Act, but I don't see why a provision concerning only the Supreme Court would be included that act. That said, either case would be possible.
Regarding the Official Languages Act, I imagine you're referring to the amendment—section 16, I believe—that exempts the Supreme Court from the person being tried's right to be heard in their language by a court created by Parliament. It would be a possibility, but it could lead to the following situation. If a court judge doesn't hear cases in French, the judge wouldn't be able to hear cases from Quebec, including constitutional cases argued by a francophone party. This may be undesirable, in the sense that, for the parties arguing before the court, the door could be opened to strategic choices related to the language used. The parties could see an opportunity to control which judges hear their case. This is undesirable.