I was flying to San Francisco one day at Pearson and was faced with a similiar situation. I was turned down and asked to be withdrawn. I had all the necessary paper work and even brought my degree / lawyer look over my papers.
I've seen people go YVR-YOW-ORD-... just to avoid going through either YVR or YYZ.
TNs are best requested when you don't have a plane to catch in an hour.