A vague letter may leave the professional duties and intended temporary stay unexplained. An ongoing position is not itself disqualifying. Describe the actual work, qualifications and period of entry requested accurately, and obtain counsel’s review of temporary intent rather than rewriting a continuing job as a fictitious fixed-term contract.
Give the officer the elements the classification requires
The classification turns on citizenship, a qualifying listed profession with its precise credential requirements, prearranged professional employment, and temporary entry. A letter that only confirms someone has been hired addresses none of these directly. Duties written in specific terms, tied to the profession claimed and to the applicant's qualifications, do more than any amount of general praise for the candidate.
The TN regulation permits a Canadian citizen to work for a foreign employer that provides prearranged professional services to a U.S. entity. The category covers professional agronomic work, and an officer will accept that advising growers on seed selection, trials and soil management is that work even when it leads to sales. Before finalizing the offer, match the real duties to one particular profession on the USMCA list; an undecided site does not permit a generic role description.
The officer decides on the letter and the degree, not on what the job is called internally.