Very good questions, my friends. I can speak from experience as the sponsor sending additional documents from Canada:
I have sent Islamabad and then London numerous emails with additional documents such as ruksati/valima/ post marriage pics, along with emails, viber/skype/whatsapp plus my boarding passes/bag tags/e-tickets, gift receipts etc etc etc .... and they have added it to our file ... GCMS notes confirms this.
SO yes, as a sponsor from Canada, you can send additional documents ONLY IF you attach the IMM 5476 (Use of a Representative Form - must be signed by both sponsor and principal applicant) everytime you email ... I have a scanned signed copy of this form and I use this everytime I ask CIC status of my file, and whenever I send additional documents.
Now, if you are the principal applicant, you don't need the IMM5476 form because you are the primary applicant
all you need to do is mail or email add. documents to CIC ... just be sure to indicate your identifying credentials such as full name, date of birth, country of birth, file number, and UCI.
