After the proceeds have been distributed and traced, the purchase agreement and escrow are signed, and the seller's records are in hand. The interview should be the last step, timed to the closing date the agreement fixes, not the first.
Sequence the money, the contract and the interview in that order
The land closing produces the funds; the corporate distribution and bank transfers produce the path; the purchase agreement with escrow produces the irrevocable commitment; the seller's statements, payroll and franchise agreement produce the evidence of a real, non-marginal enterprise. Only when all four exist can the E-2 package be assembled, and only then should the consular appointment be requested. Appointment availability at Canadian posts varies, and E-2 cases are typically reviewed on documents before an interview, so a realistic plan allows several months between the land closing and the takeover.
The purchase agreement's closing date should be set with that in mind, or made to float with visa issuance. The couple should not move to the United States on visitor entries to start running the shop while waiting; visits to inspect the business, meet staff and sign documents are permitted, and managing daily operations is not. Once the visa issues, the escrow releases, the shares transfer and the couple can take over on the day they are admitted in E-2 status.