Here is what is illegal:

84G (1) Any person who knowingly or intentionally, not being a manufacturer of mobile telephone devices or authorized agent of such manufacturer, changes mobile telephone equipment identity, or interferes with the operation of the mobile telephone equipment identity, commits an offence.

This is subject to interpretation, but Identity of a mobile phone is agreed by reasonable people to mean IMEI. Most unlocks do not tempter or change the identity of the equipment.

Alvin, it is difficult to proof all things that are NOT illegal, so we just deal with proofing what is illegal.