I did look into this. The first few constitutional experts I contacted said they had no clue.
Eventually I did get Professor Yasmin Dawood, with the faculty of law at the University of Toronto, and she gave me a more robust answer. I'll read that now: “Much of the operation of Parliament is governed by constitutional conventions and my guess is that the one seat, one vote rule is one such convention. That being said, there are hints in the constitutional text on this rule. The preamble of the Constitution provides that the Constitution is similar in principle to that of the United Kingdom and the division of representation by region is also premised on the one seat, one vote rule. Conventions are not usually justiciable, but the Supreme Court's recent decision in the Senate reference makes it clear that a change to the Constitution architecture may amount to a constitutional amendment, which, depending on the nature and scope of the amendment, could be implemented by Parliament unilaterally, or under the 7/50 formula with substantial provincial consent, or under the unanimity principle, and it is my view that most likely if it is a constitutional amendment, it will be Parliament acting alone.”