If you sent your application to CPC-M, and provided an email address, you should be receiving an email (includes approval) and mentioning the file number, and saying that it has been transferred to the Visa Office.
Our case was filed on March 30,2012 at CPC-M.
Email received on July 3, 2012 - Sponsorship approved - File number assigned - case transferred to Visa Office abroad. (not Islamabad for us)
(eCAS is updated accordingly as well.)
So just 1 email, it mentions the date they received your application, tells you you're approved, gives you the file number, and tells you about where your file is transferred, how to check status, contact info of visa office, etc.
(Note however, our approval email came from CPP-Ottawa even though case was sent to CPC-M.) I guess they must be sharing files between CPP-O and CPC-M to move things faster.
So those that provided email address, you will get an email, not a letter.
If you did not give an email, then wait for the letter.