Converting your Commercial/multi/Instrument is pretty easy. You have take a 40 quesiton written test for the Commercial and Instrument and you can have the FAA one. You don't need any checkride or anything.
Now as for working here it just depends on your luck. I know a few people who have gotten lucky, but haven't heard anybody getting their greencard through airline yet. I had the same problem. I tried all regionals. Most cancelled my interview as soon as I told them I need help with that. One turned me away once I got there cause I never told them. The last one I tried they called and said you must not even submit an application unless you have at least a green card.
But I must tell you if you are Canadian you are in better luck. US and Canada have some sort of treaty. Canadians can get US work permit or greeencard much easier than most other nataions.