Can I ask what status you are in now? You can't file for TN if you aren't currently in status. B2 is a valid status.
The I-129 is the employER's petition. THEY petition for you. Also, they will need to pay extra $1000 to allow you to start in next 2 weeks rather than 3-4 months.
Wouldn't it be more simple to get them to write a letter for you, and you go to border?
Based on the question you just asked, I anticipate you will coming back here with lots of questions on how to actually fill-in the I-129. save us, by actually readin the instructions first.