Proof of Canadian citizenship, the credential the occupation's own rule requires, and a letter from the American employer that names the listed occupation, describes the duties in concrete terms, and states salary, dates and reporting line. Anything not in English needs a complete certified translation.
The letter is the document that decides most cases
Credentials are usually straightforward; letters are where files fail. A usable letter gives the American entity's legal name and address, the applicant's full name and Canadian citizenship, the occupation exactly as Appendix 2 words it, the specific professional tasks to be performed, the salary, the period requested up to three years, and the person to whom the applicant reports. Hypothetical example: Elise, a veterinarian whose draft offer described her as an incoming partner, needs her letter to state plainly that she is engaged as an employee.
Documents in French require a full certified English translation with the translator's certification of competence, under the general evidentiary rule at 8 CFR 103.2(b)(3). Hypothetical example: a registered nurse from the parish carries a letter naming her position as clinical coordinator with no clinical duties described, and the officer cannot match that title to a listed occupation or to nursing practice. Where an employer is unwilling to put the duties in writing at that level of detail, the reluctance is itself worth understanding before anyone travels.