You would require at least a work permit (like a green card), just as a Canadian requires one for the States. You'd think it would be easier for you guys considering we're all in this NAFTA thing, but that is generally not the case. The license and ratings transfer over pretty easy, but you'll have to be current and produce your log book and the paper work for the check ride you last did (within six months the last time I transfered a US rating to my Canadian license). The first rating I put on my Canadian license was done at Flight Safety and I did not have a US ticket. I just had a letter made up by the FAA examiner and that was good enough, so from that I gather that the MOT and the FAA have a pretty cozy relationship. You might also have to write both ATPL exams though. It's been a while for me so best to phone them or try the Transport Canada web site.