A dated copy of the official instructions, his identity and civil documents, the family members he would include, a record of prior U.S. entries and any on-site work, and a written list of questions for counsel about eligibility, admissibility and tax. After the initial application and fee, USCIS sends the follow-up form and supporting-document instructions.
Work from the dated source
Because the official website states that applicants receive further USCIS instructions after the initial application and fee, a complete evidentiary file cannot be assembled in advance. What can be prepared are the facts any later instruction will require: passport and birth records, marriage and children's records if they are included, an employment and business history, and a candid account of prior U.S. entries and what he did during them, since a consultant who has performed work on site as a visitor has a fact that vetting may examine.
Print the official instructions with the date read and keep them with the file, because the framework's terms are recorded from a dated source and may change. Do not adapt an EB-5 or a TN file as though it were this one; the questions differ. Before any payment, obtain tax advice on the treatment of a gift to a foreign treasury and on becoming a U.S.
resident with a Québec consulting business, since the immigration source does not address either.