You can send anything using webform. For ' use of Rep' from the drop down choose that and fill other options accordingly.
any other form, use the sponsorship from dropdown, fill other options accordingly, and also write in the body explaining the reason.
After that, attach the file, I would suggest to attach the email/letter of CIC too so that they understand why are you providing that.
I sent my dad's death certificate this way as The fax no they provided was not working initially. Hopefully it helps.