If you want to prepare for uni, i sugeest that you take a look at this math review:
Also, you could go here
and see what courses you're gonna be taking in first year. So if you click on "chem 1e03" it's gonna show you the topics covered in the course. In that case, you could go to youtube and watch vids about a specific topic (e.g. "reactivity" or "electrochemistry ").
I found an online course outline
for phys 1d03. Again if you are interested, you can watch some vids related to the topics covered in the course.