If you want to do research in Physics after engineering, you will be required to take Advanced GRE which will include a physics exams in addition to usual GRE exam. This is true for US universities. I don't know about Canadian univs. You will also have to take IELTS or TOEFL english language test to show that you can know proper English to be able to use in college etc. As far as GPA is concerned, that depends on university & professor who choose you and at what GPA they are satisfied. Especially your performance is physics related subjects will matter, if not the whole GPA for all subjects.

you may have bigger chance in the US if you are educated enough.GRE is a must to show u qualification,