How does a high school student apply for a university in Canada?
Universities everywhere know that. They have been doing it for over 100 years. You apply last sting tne courses you are taking as a high school senior. They give you a tentative acceptance based on your grades so far. Then as long as your grades do not fall too much between now and graduation you are fine. But if your grades nosedive they may rescind your acceptance. You should ask questions like this with your school counsellors as they are paid to advise students on this sort of stuff.