Teacher certification is a provincial / territorial responsibility, as a result the process varies from one province/ territory to the next. You may work as a substitute teacher in Nunavut with or without a Bachelor of Education (B.Ed), however to be paid as a certified substitute teacher you will need to go through the application process. Please contact your principal, who can put you in touch with the Human Resource Officers at the RSO/ CSFN (Regional School Operation or Commission scolaire francophone du Nunavut), who will give you access to the appropriate paper work to get certified.
Teacher certification is also much more than a pay level, it requires rigor on the employers part in assessing levels of education, teaching qualifications, that the teacher is in good professional standing with other provincial /territorial teacher certification organizations and that they have no criminal record or have not been disciplined as a teacher in another jurisdiction, or had their professional teaching certificate suspended.
Sub teachers must follow the same application for teacher certification as teachers on regular contracts. Here's a copy of the NTA's sub-teacher guide for more information.