@TC63You will need to contact the original carrier of the iPhone with your account information with that carrier to get the phone unlocked. If it is a Canadian phone, the carrier is obligated to unlock it for you provided you are the original owner.
Depending on the age / model of your phone (if it is iOS 10 or up), it will could be done over the air with wifi. Apple doesn't use unlocking codes, every iPhone and the related activation / lock information is kept in their central database.
Or use paid 3rd party unlocking services. Public Mobile expects users to bring network compatible phone per the Terms of Service and doesn't provide phones, hence they don't provide unlocking service.