I think the issue of distribution of seats is very much tied up in the powers of the Senate and how the Senate uses those powers. This is why, in 1982, it was agreed that any changes to the method of appointing senators or the powers of the Senate should be dealt with through the general amending formula. The effect of having elected senators would alter the behaviour of senators in a number of ways. Some we can tell ahead, some we won't, but it's more likely than not that they will feel more emboldened, so the level of interaction and amount of legislation they amend and the position they take on bills that come from the House of Commons will probably be more strident than it is now.
Having more powers and more of an influence in the policy process, provinces across the board will be concerned about their representation and how many hands on that power they have. This is why I feel, from a constitutional point of view, the Supreme Court would be sensitive to this issue, and a bill that might have an effect on the powers of the Senate would be something they would say should be protected, or is protected, under the amending formula.