I was in this situation last year! Was accepted to Waterloo MPS but then I got a one year municipal gov contract I’d been waiting to hear on. So I asked Waterloo if I could accept and defer a year. They were understanding, but wouldn’t approve my deferral as it wasn’t medical.
I reapplied this year and got in earlier at Waterloo, and Queen’s as well! So I think you can probably bank on them accepting you a year later, but deferrals are case by case for most programs!