Clarification on ON procedures. Offers typically are open until April 1. At that point, you can accept an offer provisionally, but if you have received other offers, those offers are now gone. Any outstanding decisions will remain open. You may only have one provisional acceptance. Your provisional acceptance will automatically become firm on July 1, 2021.
I'm not sure how it works in BC, but in Ontario you can accept at a school (school A) anytime before June 1st and all your offers still remain open. However, if you decide to accept a different school (school B) before then, you can't then go back later and accept school A if you change your mind. June 1st is when whatever school you've accepted at that point becomes set in stone and you can't change again.
My guess is that it would be at the very least similar, if not the exact same. The dates might be different though.