I do not know where you are seeing that you need to file the 5481.
If you start at the page to get the application to sponsor spouse (and dependent children, if applicable) you get this:
https://www.ircc.canada.ca/english/information/applications/spouse.asp
No IMM5481.
If you start at the page to get package to sponsor "My dependent child
only" (my bold), it does ask for the IMM5481.
But clearly that does NOT apply to your situation, and if you'd read the instructions carefully you'd not be asking.
So I'm stumped why you think you need this form.