Owning and drawing income from a Canadian farm operation is not United States employment, and a dependant in TD status is not prohibited from having Canadian income. What TD does not allow is working in the United States, including remote work performed while physically there, and the tax treatment of any income is a separate question for an accountant.
Separate the income from the activity
The distinction that matters is where the work is performed, not where the money comes from. A spouse who retains an interest in a Canadian farm corporation and receives dividends is not working in the United States by doing so. A spouse who sits at a kitchen table in the United States doing the books, ordering inputs and managing staff for that same operation is performing work while in the country, and the fact that it relates to a Canadian business does not by itself resolve the question. Have the specific arrangement reviewed rather than assuming either extreme. Then ask an accountant about residency, withholding and cross-border filing obligations, which will apply regardless of how the immigration question is answered and are easier to organize before the first payment than after a tax year has closed.
Hypothetical example: a seed-pathology analyst plans to live in the United States while her partner continues operating an online bookkeeping service for Canadian growers. A first review lists where each task is physically done, who directs it, and which status authorizes it. Client location and payment currency do not settle permission to work while present in the United States. The partner should obtain advice on the proposed work before relying on remote routines. Keep the immigration analysis separate from tax residency, payroll and licensing questions; each uses different records and may produce a different answer.