With your study permit having been approved before March 18 makes your US stay actually a moot point. As long as you can satisfy the border agent that your travel is essential you are good. You apparently did that and I am truly happy for you. Enjoy the privilege, I need to wait longer and can currently not enter.
Hi. I was on the US F-1 student visa. I'm not sure about the lastest update for US students since I have my visa approved before March 18. The CBSA did asked me about my status in the US though. They were easy on me maybe bcause Winnipeg airport is small and not many visitors I guess.