I brought all the documents that on the online checklist, including the official letter from school, the official transcript, and I also brought my diploma in case they wanna see it.
Yes, I paid 255 again, the CBSA and CIC are not the same departments, so you have to pay again, but after you successfully got the permit at the border, you can withdraw your online application and get a refund if they haven't yet started process your application.
You don't need to have a U.S. Visa, even you have one, you still don't want to enter the U.S. You need to tell the U.S. Customs that you don't want to enter and they will issue you a flagpole, you will need it at the Canadian immigration in order to let them accept your application.
Yes you need to leave Canada, but technically you are not going to another country either, although when try issue you the flagpole, you are on the U.S. Soil.....