Social Security Number

You can go to work after you get a work permit. Then go to apply for a SSN number. Will get it in two months. During this period, the employer can't pay you.

Or you can wait for the SSN then after get it, go to work.

Between Canada and USA, there is a treaty for social security payment. So you don't need ask the social security payment back when you leave this country. I guess the same in reverse aspect.