The actual TN process is incredibly simple once you qualify, the grey area here I suppose is the category that you would come under under the NAFTA professionals list.
ACCOUNTANT Baccalaureate or Licenciatura Degree; or C.P.A, C.A., C.G.A., or C.M.A.
ECONOMIST Baccalaureate or Licenciatura Degree
MATHEMATICIAN (to include statistician) Baccalaureate or Licenciatura Degree
These are the 3 that stand out to me.
the actual process is easy and does not need a lawyer, unless they have the money they're willing to spend. Your employer needs to write a DETAILED letter that you can present at the border and be processed there. It should outline the work you will do, daily duties and responsibilites, the impact you will have, why you are the best person for the job, why you are a skilled professional etc. Then you bring your offer letter as well as copies of your degrees.
TN visas are granted 3 years at at time and can be renewed indefinitely.
The other option is H1B, which is dual intent. If your employer is CAP exempt, then they can file for you at any time. If they're cap subject, it won't be happening this year.