An academic curriculum at Canadian high schools is usually a bit different from the one at American high schools. If you apply to one of American universities, then I would recommend you to consider American high school. From my past experience, even when the best students in Canadian high schools are transferred to an American high school, they tended to struggle, especially in subjects such as advanced math and science courses which lead to lower grades.
You can also prepare university admission process while you are still at a Chinese high school. What really matter is how to prepare and present well about who you are to universities in the application process. This might need some time, energy, and of course careful planning. I suggest you to start as soon as possible by reviewing your current courses and by looking into possible universities that might interest you. Also consider to get some professional advice from school guide counselors or professional college counselors. This assistance would be very helpful as you prepare for college admission.
