Canadian citizenship, a prearranged professional nursing position, and the licence the listing names. A health care worker certification and the destination state's own licence are additional practical conditions.
Three authorities, only one of them immigration
The appendix entry for registered nurses accepts a state or provincial licence, or a licenciatura degree, so a nurse licensed in a Canadian province already holds the qualification the category asks for. That is only part of the answer. Admission in a health care occupation of this kind also requires a certificate confirming education, licensure, English proficiency and examination, and the hospital cannot lawfully employ a nurse who is not licensed in the state where the work is performed.
Alongside those sit the ordinary conditions: Canadian citizenship evidenced in the applicant's own name, a prearranged position with a U.S. employer, duties that are genuinely professional nursing, and temporary entry judged from the employer's stated period. Self-employment is not permitted, and any ownership interest in the employing entity must be disclosed.