When I took a job in the US, the day before my flight I drove to Niagara falls to get my TN. I was turned down the first time (fingerprinted) and sent back home. I revised my paperwork, went a second time (the same day) and was told I needed one small change in my documentation and was assured that once I fixed that small thing I would be able to get my visa OK.

So I took the chance and I had no problems getting my TN at Pearson. But I am very glad I took the time to sort out the problems ahead of time.