Diocesan priests are considered to be employees and are responsible for providing for their own retirement, just like anyone who works at a job where there is no pension plan (like my place of employment).
In Canada, diocesan priests are paid a salary and pay into the Canada Pension Plan (that’s not optional for anyone and is a percentage of your income). Granted, since they are not paid very much they don’t pay much in – but the salary varies by diocese. I’m pretty sure a priest in outport Newfoundland and Labrador is not paid the same salary as a priest in Toronto.
I’m not an expert on all dioceses but I know that priests in my diocese are also encouraged to pay into a Registered Retirement Savings Plan (similar to a 401K, I think) and the diocese will collect the money and do that for the them.
If they’re smart, while they are young they’ll also get health insurance that will pay for medication & eyeglasses and unforeseen medical expenses such as physio-therapy. Regular visits to the doctor or hospital admissions are covered by our universal health care program.
Upon retirement they would collect CPP, Old Age Security, the returns on their own private plan and, depending on how much that totals, they might also collect the Guaranteed Income Supplement.
That’s not going to allow them to live in luxury, but it’s no different from someone who’s lived hand to mouth all his life at minimum wage jobs.
My diocese also has the “Shepherd’s Fund”, money which is collected from parishioners and invested to provide priests with money they many need for emergencies.
Most retired priests offer their services to celebrate Mass in parishes where a pastor wants to go on holiday or on retreat and they will often celebrate Mass for groups having special celebrations (one did that for us when we had our family reunion.)
Religious priests, of course, are cared for by their order/congregation. They would receive the Old Age Security but that would most likely be turned over to their bursar and they would be given an allowance.