Then why on the guide (IMM 3999E) it says:
Translation of documents
Any document that is not in English or French must be accompanied by:
the English or French translation; and
an affidavit from the person who completed the translation; and
a certified copy of the document.
Note: An affidavit is a document on which the translator has sworn, in the presence of a commissioner authorized to administer oaths in the country in which the translator is living, that the contents of their translation are a true translation and representation of the contents of the original document.
Translations by family members are not acceptable.
In the IMM 3999E guide that you mentioned, you didn't read the entire note, it states:
Note: An affidavit is a document on which the translator has sworn, in the presence of a commissioner authorized to administer oaths in the country in which the translator is living, that the contents of their translation are a true translation and representation of the contents of the original document.
Translators who are certified members in good standing of one of the provincial or territorial organizations of translators and interpreters of Canada do not need to supply an affidavit.It sounds as if you have one that is already certified, if you do - you do not need an affidavit.