I'm a single mum myself, and I really feel your pain on this one. I agree that it's unreasonable to require this document if full custody is explicitly stated in court documents and you have no contact with your ex. Often there are DV issues at play or even a protective, order making it difficult, dangerous, or even impossible to obtain this kind of notarized permission. Fortunately I was lucky enough to be able to get the form, but I know plenty of people who wouldn't even know where to begin to locate their exes. Like being a single parent isn't hard enough without jumping through yet another hoop!
Having said all this, the law is the law, and if the goal is to immigrate to create a better life for you and your child, then I'd do whatever was necessary to satisfy the requirements. Can you talk to a family law expert or directly to someone at CIC? Best of luck to you, and I hope you keep us posted.
