Many Thanks for your prompt and complete advise Marlee and Luc22!!!
After reading your posts, I think I will take an approach just in the middle! will not send before receiving AOR / E-Cas Number but will not wait for Sidney to ask for it either.... with the E-Cas number on hand it will not get lost, even if I send before they ask for it.... And they will ask for it anyways! so the document will be already there when the review of my file is in process....
At first, had doubts about sending before receiving the request from the Immigration Officer, because of the instruction "Do not Send Additional Documents Unless Requested". But like Marlee said the document has already being requested! it is not an "additional document".... so this is a more than valid point.....
Also, on a letter I submitted explaining why I had not send this document with my initial application, already stated that I would send it immediately after receiving it, so, when reviewing my file, the Immigration Officer should at first check if this item has already arrived at the Immigration Office so he/she can complete the review (if he wants to move things fast). And if he/she doesn't, the document will already be there whenever they search for it.
What I will definitely not do is sending before getting AOR.... here I will buy Luc22's advise.....
Many thanks again for your help and Merry Xmas / Happy Holidays!.
MontréalSW