GA Flight Instructor with student reported an NMAC during approach to AUO airport requiring evasive action to avoid a possible collision.

Narrative

I was on a VFR flight with a student and requested Vectors to Final RNAV 18 into AUO with the approach controllers. Approach had us on a 070 heading at 3500 MSL for vectors to the final approach course. Aircraft Y was approaching the same approach course from the NE at a much higher speed. They cut across the final approach corridor; continued a clockwise turn to rejoin the approach course at a lower speed and altitude. We did not have visual contact with Aircraft Y when our avionics gave a traffic advisory alert. As a result we turned hard to the right to avoid their perceived flight path. As we were turning Atlanta Approach gave us a traffic advisory call. I believe Aircraft Y was on an IFR Flight plan and cancelled when they had the airport in sight. I believe poor descent planning resulted in them being too high and fast to make a straight-in approach normally; resulting in them making a wide sweeping turn and cutting us off to bleed airspeed and altitude.I have not spoken with the crew of Aircraft Y so I cannot confirm my suspicions regarding their flight.