Hi Veena,

Yes it is possible to do phd in mathematics in Canada with a GRE score, but that is not the only criteria for getting an admit as Universities will look at other major factors such as your research work in the field of interest i.e if you have any research publications in any national or international journals, your masters GPA etc. 

Note - Not all colleges in Canada require a GRE score for admissions in phd program, do check the admission requirements of the colleges that offer the course you are interested in. Though TOEFL/IELTS is a necessary requirement in all the colleges as a proficiency in English language test.