Currently Catholicism has the highest concentration of believers in Canada followed by Protestantism, and then significantly less concentrations of Muslim, Buddhists, Judaism, etc. Since Canada is so multi-cultural, practitioners of most religions can be found somewhere in the country.
Canada is an ethnically and religiously diverse country, in which all of the religions of the world can be found. The religion with the largest membership is Roman Catholicism. Another major religion is the United Church of Canada. Based on recent immigration, Islam probably qualifies as #3.