Proof of Canadian citizenship, the employer's letter describing prearranged professional duties, and the credential evidence the listed profession requires. Everything else supports those three.
Three documents carry the case
Hypothetical example: The citizenship evidence should be current and in the form the applicant will actually present, not a copy of something being renewed. The employer letter needs to describe the position, connect it to the named profession, state the period sought and set out the terms; it is signed by someone with authority to bind the employer. The credential evidence must match the rule for that profession, which may mean a degree plus an equivalency assessment, a licence in the state where the work will be performed, or documented experience where the Appendix permits it.
Supporting material — a résumé, project descriptions, a corporate profile — helps an officer understand the work but does not substitute for any of the three. If one of the three is still being processed, the file is not ready, and travelling in the hope that it will be treated as a formality is the most common avoidable failure.