The offer letter on institutional letterhead naming the accredited college, the department, the course level, the dates and the pay, together with the degree itself. If the diploma is in French, add a complete certified English translation.
Two documents carry the whole case
The port-of-entry officer or the USCIS adjudicator has to be able to see, from the papers alone, that the employer is a college and that the work is college teaching. The letter should therefore say the institution's full legal name, that it is an accredited postsecondary institution, the courses to be taught and to whom, and whether the appointment is for one semester, one academic year or longer. A generic human-resources template that only gives a title and a salary can turn a clear case into an argument at the counter.
The second document is the degree. The teacher entry requires a baccalaureate in any field, so the bachelor of science alone suffices; bringing the bachelor of education as well does no harm. If a Québec diploma or transcript is in French, USCIS regulations require a full English translation with a translator's certification of competence; include the same complete certified translation in a port-of-entry package.
Carry the originals and copies of both.