Paid vacation and a new employer

Suppose your employer gives you 3 weeks of paid vacation per year. You take 2 weeks in May. And in a couple of months later, you resign. What happens with that 1 week? Do you lose it, or do they pay you 1 week extra?
And what if you go to your new employer, and he also gives you 3 weeks/year. But you already took 2 or 3 weeks earlier that year with your first employer. I assume that doesn’t affect the new employers vacation?

(don't know if it's depending on the province, but in my case, it's about Ontario and a non unionised job)