I do not really think that notarizing adds much weight to a document. Either it's a legitimate document or it is not. I think those at IRCC who adjudicate these applications have a good nose for what is genuine and trustworthy.
The only form of "notarizing" that adds much clout to a document is when the document is put in solemn form, such as an affidavit or a statutory declaration, where the deponent swears to the truth of what they are saying. But, as a practical matter, for someone in a foreign land to swear a false declaration really exposes them to almost no risk.