I'm not sure I understand the point of reapplying online if your first application is refused. But you certainly can if you want to.
No - you cannot get a TRV at the border. CBSA does not issue TRVs.
Question for you if you're able to answer for my sister, that would be great....
I know on their website it mentions that you can only be part time during the final term of your program but how about your course sequence doesn't allow you that and you become part time for only one term during your masters? but not the final term.
Also I think every university has their own full and part time statuses. For example for University of Ottawa, their full time status is 2 courses on Masters level and 4 courses on undergraduate level..... So do they consider each university's different full and part time standards?
Also if in the letter of enrollment, it mentions that you have been enrolled full time throughout your studies, would that help as well?