Many fear opening up the Constitution out of fear of getting bogged down in the unity debate. Because of this, we certainly cannot rock the Constitutional boat too much or propose any radical changes. But I'd immagine it should be possible to propose moderate changes to the Constution that would not bring about too much opposition from anyone and that could even rally all parties around a few moderate changes. Among them:
1. Abrogating the separate school system. Ontario might oppose it initially, but considering the PQ has now painted itself into the 'secularist' corner, the PQ would look ridiculous in opposing such an amendment. And if Quebec supported it, it would look ridiculous for Ontario to then oppose this at the risk of further Constitutional instability, especially in light of the UN having criticized the separate schol system. The Green Party would undoubtedly support this, along with the NDP no doubt. Some conservatives support funding all religions or school vouchers, but just striking the separate school system out of the Constitution does not necessarily impede on that at all. As to what to replace the separate school system with, Ontario would be free to implement the system of its choice, just not favour particular religions anymore, so conservatives ought to have no issue with that at all. Plus striking down a Constitutional article would not cost money so the political right has nothing on it there either.
2. Entrenching at least the negative right to the local indigenous language. Quebec's main argument for Bill 101 is protecting the linguistic minority. Certainly the local indigenous language is far more endangered than French. From a PR standpoint, Quebec would have no choice but to support such an amendment, forcing it to exempt the local indigenous language from Bill 101. Since this would not involve positive rights as in the case for English and French, the argument that it costs too much would be a moot point. And how could any party oppose the negative right to the local indigenous language in light of the significant positive rights to English and French in the Constitution?
I don't see why no political party could not come up with a list of amendments it would propose to the Constitution that no party could oppose short of political suicide, while leaving anything too controversial or divisive out of it. I've just given two ideas above, and I'm sure some here could probably come up with a list of others that some party or other could promote as a moderate step in the right direction.