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Not essential. Do it if it will make you feel happier about the application. You can get it notarized by a commissioner of oaths or at a lawyers. Certain Service Ontario's (dont know where you are located) offer commissioner of oaths services.

I am sure you have asked this question before.
 
Is this form a mandatory form? If it’s an optional form, why are you filling it. And sorry, if i misunderstood anything here.
 
What’s an ITN?