Why not let them separate?
I think Canada has simply been left behind by the times. The experience of EU shows that countries can achieve significant economic and political integration while keeping cultural autonomy and that is what everybody cares the most about anyway. They all want to be able to dictate domestic content on TV and radio and preserve the cultural uniqueness (and the right to smoke in restaurants and such).
Free movement of goods, people and capital can be achieved (or in the case of Canada maintained) with little or no effort. Securities regulations are already separate by province and the same with educational and health systems. As for the military, even by its own self-understanding, the future role of the Canadian military is not in the function of defence of Canada (from whom?) but rather in maintaining Canada's position on the world stage in terms of international response to disasters or contribution to peacekeeping. For that role a loose coordination of the military between Quebec and the rest of the country would suffice.
The benefit of separation would be great for both Quebec and the rest of the country. The rest of the country could drop the costly and cumbersome bi-lingualism which nobody is really emotionally into. Quebec would get that which it has always wanted and that just might lead to a renaissance and a re-juvenation of sorts.
Objectively speaking, Canada and Quebec could devolve to an EU type of arrangement with minimal disruption or cost. The fears of "disintegration" as a consequence of separation are without basis today, and it is doubtful they were much more valid a decade or more ago.