Proof of citizenship, the original credential the listed profession requires, and an employer letter that states the profession, the duties, the pay and the period. Anything the officer cannot verify from those pages is a question the applicant must answer on the spot.
Prepare for the question the officer will actually ask
A port-of-entry application is decided in one sitting, so the file should answer the predictable questions without argument. The employer letter should name the Appendix 2 profession, describe the duties in the employer's own words, and state the salary, the start date and the intended length of stay within the three-year maximum period. The credential should be the original or a certified copy, with a transcript when the degree title alone does not show the field.
If the degree was earned outside Canada, Mexico or the United States, bring the evaluation. Include the previous passports if earlier U.S. entries or refusals exist.
Hypothetical example: an East Hants applicant brings a letter that calls him a 'Field Operations Lead' while the credential is a science degree; the officer has to guess the profession. A letter that says 'Agriculturist' and lists agronomic duties removes the guess. Keep a second copy of everything in the vehicle or bag separate from the file presented.