The United States took the TOEFL, and now many American universities accept IELTS scores. Canada can take IELTS or TOEFL.
Applying for an American university requires the SAT, which means that high school graduates need to take the exam.
SAAT, entrance examination for middle school students in Canada and America. ACT American college entrance examination
As for what you want to test, it depends on your specific situation. If you go to the United States to study TOEFL and SAAT, if you go to the United States to take SAT and TOEFL or ACT and TOEFL. If it's Singapore or Britain, it's ok to take the IELTS test. No matter what you take, it's a test of your English ability, just from a different angle. As for the specific required scores, you can go to the ethnic school you want to go to. Official website has specific score requirements.