具体看学校官网，比如多伦多大学Admission Requirements:
Chinese Upper Middle School Graduation Exam results (Hui Kao), if available
Senior High School (Upper Middle School) Graduation
Chinese National University Entrance Examinations (Gao Kao)
Applicants who do not present the Gao Kao must provide a letter stating the reason(s) for not sitting for Gao Kao, final results of their last three years of Upper Middle School, copies of awards received for academic achievement, results of other standardized tests (e.g. SAT, AP, IB), rank in class, supporting letters from the school, and a school profile, which includes the success rate of the school's graduates in being admitted to top universities in China, their students' other achievements and their admissions selectivity.
写理由是必须的，很多学生也是没有高考就被多大录取了，具体是否能被录取还得看你的理由写的是否充分合理。
