Sponsors are notified about their approval to sponsor, some by snail mail, some by email. Make sure you check your spam/junk folder, it has gone there for some persons. A sponsor will then have a Universal Client Identification (UCI) number, which you can use to access the electronic Client Application Status system, or the notorious "eCAS" you will see everyone post about.
When the file goes to the visa office, the applicant will also receive their own UCI, similar but not identical to their sponsor's. Mine is about 6 digits off my husband's, for example, the last two numbers in his are "86" and mine are "92". The applicant will also have 2 file numbers, the B file number (the paper file) and the F file number (the GCMS file). If the applicant receives an Acknowledgement of Receipt (AOR) from the visa office, they may get either or both of those file numbers specified in the AOR. Sometimes visa offices don't bother sending AORs, especially if they process the file quickly and don't request the passport upfront, like most of the western hemisphere offices.
A word on eCAS. It is NOT gospel. Its contents are very uninformative and what little goes there depends on the visa office you are being processed through and how diligent your immigration officer is at updating the thing. For example, my own experience is that for 9 months it sat at "Application received" and by the time it went to "in process" they had already sent me a letter requesting new medicals and police records. I have now received my visa, but it has YET to update to "Decision Made", and my address has not been changed to my husband's, as has happened for others in the same situation.
Please do not frazzle yourself if nothing happens in eCAS, nor be too excited if something does happen. Sometimes there have been mass updates from visa offices worldwide, when it seemed many persons were making progress, and then nothing happened for months afterwards. They tweak the system often, so don't be too surprised if "updates" happen and then...nothing. Just get on with your life, let CIC get on with their work, and it will all come out in the end.
