What is London asking from you? If the documents they are asking (or if you are sending additional documents voluntarily) and they are adding to 70 pages worth 3 MB, it is perfectly fine.
I have emailed London (on their
LDNIMMIGRATION @ INTERNATIONAL.GC.CA) 50MB worth of pictures, documents, ongoing proof of relationship, each email weighing 10MB on average and GCMS notes confirmed they added these on file. CIC also has the ability to condense the size of the file as one officer made a comment 'reduced pictures size to standard' on my notes.
Hope this helps.