The proposal comes from the Department of Finance of Canada, which consulted the departments of finance in each province and territory. So in a sense, there has already been preliminary approval on the part of the provinces.
As concerns enhancing the Canada Pension Plan, we can see that two-thirds of the provinces includes Quebec, if you carefully read the texts concerning the CPP.
Of course, Quebec does not represent one-third of the population, so it does not have a veto, but it is still part of the consultations. What Bill C-51 says is that henceforth, changes may be made by regulation. In this case, there would be approval by two-thirds of the provinces, but this would exclude Quebec.
So indeed, Quebec would also have to legislate separately.