yes, you can do it later.

You need SIN when you work there.
I do not know if there is any $ limit. I prefer to take a traveler check, not cash.
If you do not plan to stay in Canada, you simply destroy the check after you come back.
Sometimes, the immigration officer will not give you the maple card because you are not planning to stay. In that case, you need to call a toll-free number inside Canada on workdays to apply the card, or you can apply it when you go to Canada next time.

Good luck