I'm trying to figure the same thing out. The email mentioned that I can upload 'documents' and nothing specific about which/what. I was taking a blind shot at sending anything that might help speed things up. I only want to do it if it doesn't negatively affect my application is all.I'm probably wrong, but I wouldn't advice uploading documents other than the documents you told them were missing in the webform. They opened your application account so that you upload the loan documents so if you upload other than that they may think that you were not honest in the webform about the documents that were missing. I'm just sharing the first (unverified) thought that came to my mind, so I might be completely wrong about this.
By the way how do you send a webform?
You can submit a webform from here - https://secure.cic.gc.ca/enquiries-renseignements/canada-case-cas-eng.aspx?AspxAutoDetectCookieSupport=1