Yes, I know several poeple who did that. It's no big deal. Once you are approved... then no more hassles... all you will be asked is to do medical again. People don't want to do again medical fearing that they may fail the checkup. But my frens have done this and they faced no problem. One of them landed in Canada himself... but then he brought the wife after more than one year.... although he got visa for both of them together. For wife, she was asked to do medical again. Oh you need visa to go to USA from Canada if you are Canadian Permanent Resident. Go to US consulate and apply for visa. If you have job in Canada, take dociument to show them, it will be quite easy to get visa. If you have no job.. there is no chance you get visa to travel to USA just being Canadian PR.