Canada/Mexico TN visas for USA work stays 3 year duration

This is the easiest visa for Canadian citizens and Mexican citizens to stay as a contracted person in USA.

- an agreement signed by an employer of a USA company and a letter stating the full or part time employment opportunity is enough to obtain a TN visa.

This can be done at any custom office(international airport essiest) after arrival in USA,does not have to applied for before 1st visit. Only Mexican or Canadian citizens can do this.

The TN visa, established under the USMCA, allows Canadian citizens to work in the United States in prearranged professional-level business activities in designated occupations such as engineers, scientists, computer programmers, and other professions listed under the agreement.

Canadian citizens do not need to obtain a TN visa in advance; they can apply for TN status upon arrival at a U.S. port of entry by presenting required documentation, including a letter from their employer detailing the position, purpose of employment, qualifications, and intended duration of stay.
Spouses and unmarried children of TN visa holders may enter the U.S. on TD status, though non-Canadian family members must apply for a TD visa

https://www.uscis.gov/working-in-the-united-states/temporary-workers/tn-usmca-professionals