It should identify the distributor as the party engaging her services, name the profession, describe the project scope and deliverables, state the period and the fee basis, and identify the degree or experience relied on. It should not describe a line-management job.
Write the letter from the client's side and keep the contract consistent
Hypothetical example: the distributor's first draft says she will 'join our operations team to run inventory'. That sentence describes employment in an operational role, and worse, it contradicts the consulting agreement her corporation signed. The revised letter should say the distributor has engaged her professional services as a management consultant to analyse its inventory planning across its branches, design a replenishment and reporting process, and support implementation, from a start date to an end date, with fees payable under the agreement. Attach the agreement between her corporation and the distributor, her qualification evidence and a short résumé. State plainly that she holds no ownership in the distributor. Where the engagement is through her corporation, make sure the corporation's role is as contracting party only, and that the distributor directs the scope. Keep dated copies of each version, and carry originals of the letter and her degree or experience statements at the port of entry.
Hypothetical example: a physiotherapist accepts a fixed engagement with a U.S. therapy group, while her Canadian corporation will only invoice for administration. The signed engagement, not the invoice format, settles who controls the work and whether the role is genuinely with the U.S. group. First review should return a document index and a contradiction list before travel is booked. The group can support a port-of-entry application or file Form I-129. Neither process permits the professional to enter and perform services for a practice she owns.