Notes created by users in a Canvas course who have the role of Teacher, Principal Instructor, or Course Coordinator will be seen by students as "Instructor Notes" in Unizin Engage.
All other Canvas roles - including TAs - are seen as students in Engage. Once someone enters Engage for a course their role is set for that course. For example if a TA has already had the “TA” Canvas role and entered Engage, you can’t later change them to an “Auxiliary Instructor” to have their notes show up as “instructor notes”.
As of 12/4/18 this issue still exists.
There is currently no workaround other than to make sure a user's role in a Canvas course reflects how you want their notes to show up prior to them entering Unizin Engage.