When you get an ITA, you will get a personalized document check-list along with an upload form and button. No documents in hard format are to be sent to IRCC, all documents are to be uploaded through the personalized document check list.
IRCC does require the scan of your degree certificate at the time of uploading documents, but, not the mark-sheets or transcripts (although, you can, if you wan to).
https://www.canada.ca/en/immigratio...-after-january-1-2016-completeness-check.html