Canadian citizenship, a prearranged nursing position with a U.S. employer, and the credential the professional list assigns to Registered Nurse — a state or provincial licence or a Licenciatura — plus the federal health-care worker certificate presented at admission. A permanent resident of Canada who is not a citizen cannot use TN regardless of nursing qualifications.
Four facts decide it, and the offer letter is only one of them
Start with citizenship, because it is absolute: a Canadian passport, not a PR card, is the treaty qualification. Second, the position must be prearranged professional employment, which rules out setting up as an independent contractor to several facilities without an employer. Third, the licence: an Ontario registration meets the list wording, but the state where the hospital sits may separately require its own licence before practice. Fourth, the health-care certificate, which is required by regulation for nurses and is checked at the border. What is not required is a U.S. visa stamp; Canadians apply at a port of entry or by petition from inside the United States. Karina should confirm each of the four in writing before giving notice at her current employer, since missing any one of them stops the admission.
Hypothetical example: A Canadian respiratory therapist accepts an offer from a U.S. rehabilitation clinic. The first review compares the occupation, offered duties and required credential against the professional entry, then checks the clinic’s control over the work. The decisive records are the signed letter, licence record and any credential evaluation. If the clinic instead asks the therapist to invoice through a personal company, the relationship may fail the rule against operating independently. Resolve that before resignation, because changing the pay arrangement after review can change the answer.