if he got to the US legally, it will be very easy. If he got here illegally, it will be way more complicated. Many people say marriage to USC won't save you if you got here illegally, but it's not always the truth. I've met 2 different people a couple of years ago (they worked at the same place i did after they were legalized), who got here illegally, got married, and their attorneys worked things out that they were able to stay here, although it took them over a year.
