There is no form to fill out, because it's a letter, not a form/application.
Statutory declaration means that it is signed by the writer in front of someone like a Commissioner of Oaths and/or a Notary who is authorized by the province/country to accept such a signed-in-front-of-them document.
Finding a CoO in Canada is pretty easy, every province has a list/directory, and it's much cheaper to go to a CoO (~$5) than to a notary ($45+).
So have your minimum 2 friends (according to the instructions on your country-specific checklist) write a letter and then they have to take it (unsigned) plus 1-2 forms of photo-identification to a CoO or notary (in Quebec, I know that city clerks at city hall are authorized, I'm not sure about how other provinces do this). Then then "swear or affirm" that the contents in the letter are "true to the best of their knowledge". Then the CoO will double-check to confirm that the person who is swearing/signing is the same as the photo ID and the same as the letter states.
They do not certify the truth of the letter. They only certify that the signature-person swears that they are the same person and that the letter is true to the best of their knowledge.
My letters were only 1 page long (each) that my friends stated my full name (plus UCI # and address) and explained how they knew me and for how long they have known me, and then also how they came to know that I was in a relationship with my partner (his full name, didn't give SIN or any other ID for him in the letter). They stated that they believe our relationship to be genuine, committed. They stated how they have meet or hung out with us several times since X years ago or something like that.
Then they also provide all their contact information so that CIC can get in touch with them if CIC has any further inquiries.
