I'm not an expert on these matters... however I believe NAFTA primarily gives people in various fields the opportunity to work in the other country without needing a work visa. It may also confer interchangable credentials upon those already certified as a P.Eng.
Entry to the profession, however, is regulated slightly differently. Prior to my institution (BCIT) gaining accreditation with CEAB, our graduates had to travel to Bellingham to write the exams for graduates of foreign engineering schools (
http://www.engineerscanada.ca/e/pr_i...nal_ieg_1.cfm).
They had a 100% pass rate, if I recall correctly, so I wouldn't count this as a big barrier... but it is something to check into.
Jason