1) To work legally in the US, you need H1B visa (work permit). You lose your permanent residence status in Canada if you go work in the US before you get your Canadian citizenship. But there is always a way to solve this problem.
2) To go for the job interview in the US, you need a certain type of visa, for example, H1, H2 visa. If you are not working currently, it's not easy for you to get this type of visa.