Doing the 3+2 makes little sense - you have to get into Dartmouth, you have to leave the kids you know at Colby after 3 years - and oh by the way, you should see if you would get an AB after 5 years (not ABET accredited) or a BE (which takes normal Dartmouth kids 5 years).
As for working in the US, that may or may not be possible.
Good luck.