The most important thing they look
JOB DUTIES / DESCRIPTION
NAFTA category
min. EDU Credentials required in that category
My recent experience says- keep the letters very very short and simple dont describe 'glorify' yourself nor put too much company info ....CBP officer was very very nice, read only TN cover letter and asked me my highest edu qualification.
My TN cover letter was only two pages. brief company info, category, five-seven most imp. job duties in bullet points using layman terms- not too much technical words, pay $X annually with std benefits, upto 3 year duration, start date ' After getting TN status report to our XXX office next business day".