Yes, if the position is genuinely agronomy work and he is a Canadian citizen with a baccalaureate degree in a relevant field. The risk is the framing: a letter dominated by sales targets and commission describes a sales job, which is not a listed profession.
The profession is decided by the duties, not the title
The Agriculturist entry, which expressly includes agronomists, requires a baccalaureate or Licenciatura degree. The degree question is therefore straightforward for a graduate in agriculture, crop science or agronomy. The examination that usually goes wrong is whether the offered position is professional work in that field.
An officer will look at the balance of duties: soil sampling programs, fertility recommendations, trial design and pest scouting are agronomic; account development, order taking and quota management are sales. Many US agricultural employers combine the two, and there is no rule against an agronomist supporting sales, but the professional component must be the substance of the job. Ask the employer to describe a typical week in the letter.
If the honest description is mostly selling, TN is the wrong tool and pretending otherwise leads to a refusal that follows the applicant to later applications.