Proof of Canadian citizenship, the employer's letter, the licence relied on and the health care worker certification. Carry the state licence or permit as well, even though it is not the immigration test.
One folder, duplicated before departure
Citizenship is proved by a Canadian passport or a citizenship certificate; a permanent resident card does not support this category at all. The employer letter should name the position, describe professional nursing duties, state the licence relied on, give the salary, and set out the period of employment and the facility. The provincial licence should be current, with verification of its standing where the regulator provides it.
The health care worker certification should be the original document. Add the state licence or temporary permit, the degree and transcript, and a certified English translation of anything not already in English, since a translator's certification of competence and accuracy is expected. Where the employer has filed Form I-129 instead, carry the approval notice with everything else.
A missing item at a port of entry is a refusal rather than a postponement.