With your permission, I will begin by answering your second question. As I mentioned earlier, Parliament is sovereign, subject to the limits set out in the Canadian Constitution. This is a fundamental constitutional principle. The federal Parliament, just as is the case of provincial legislatures, is free to adopt any laws it wishes.
I also believe, subject to correction, that with the exception of criminal law, nothing prevents Parliament from passing laws that have a retroactive effect. Could Parliament pass a law the effect of which would be to retroactively impose obligations on the province of Quebec, obligations that Quebec would perhaps not have to fulfill? Even if I wanted to, I could not really give an opinion on this issue. I do not possess the necessary expertise. What one must however keep in mind is that Parliament is sovereign and that this is therefore in the realm of possibilities.