To see exact guidelines: visit the uscis.gov website. This is not legal advice.
This form is for companies hiring Canadian Citizens who seek a TN non-immigrant status to stay in the US for 3 years. To stay longer, first get the letter, then get the employer to fill out Form I-129 (see here) once you're in the U.S.
First, check if the employee's occupation is listed here in "Appendix 2 to Annex 16-A of Chapter 16 (Annotated)". The employee must also have the degree. If they don't, they will not be eligible for TN status.