I can speak to this at a very high level.
We know that only a few pension plans in Canada offer a survivor benefit to a spouse or common-law partner whose union begins after retirement. As you pointed out, there is the Quebec plan, but there is also the Ontario Municipal Employees Retirement System, both of which have those. In both cases, the benefit is provided to the spouse at death and is only provided to that one survivor. That's to say that a married spouse would have priority over a common-law spouse in cases where a plan member was, say, separated at the time of death.
Even in plans that may offer that postretirement benefit, there are still obviously some eligibility restrictions. That means the person living with the member may not, upon their death, receive a survivor benefit.
It should be noted that these plans provide a benefit that's a percentage of what the member was receiving rather than a percentage of an unreduced pension benefit, which is what we offer under the public sector plans here in the federal government.