TD status permits him to accompany you and to study, but it does not authorize employment. Managing a Canadian business from U.S. soil is work, even if the customers and the payroll stay in Alberta, so the plan needs its own assessment rather than a quiet assumption.
Remote management is still activity that needs a permission
The TD category exists to keep families together; it does not carry work authorization, and the question of whether an activity is employment is answered by what the person does, not by where the employer is incorporated or which bank pays the salary. Directing staff, negotiating seed contracts and approving invoices from a U.S. address are the ordinary duties of a business manager.
A spouse who intends to do that regularly should be assessed for a route of his own, and the options depend on his facts: if he is a Canadian citizen with a listed profession and a U.S. employer he may have his own TN, and if the seed company opens a U.S. affiliate he may qualify as a transferee after a year of qualifying employment.
Short visits home to run the business are a different pattern and should be planned deliberately. Children may attend school in TD status; a child who turns 21 loses derivative eligibility.