After you submit the GCMS request, right away you will receive an email which has this message;
(1) "Your temporary request tracking number is 1234567. After your request has been registered, a new number will be assigned to your request."
(2) A PDF attachment with a copy of the payment receipt which has the number R123456789 (if GCMS is requested using the Access to information Act)
This temporary tracking number will eventually change to something like this "IRCC ATIP file 2A-2019-12345" but you will only learn of it from IRCC (1) when you receive the GCMS file (2) if there is going to be a delay or (3) if IRCC has questions for you. Until then if you need to contact IRCC about your request (if it's been more than 30 days and you have not heard from IRCC) you can use either the temporary request tracking number or even the payment receipt number.
By law IRCC is required to notify you within 30 days if they need more time to process your request. If that is applicable then you will receive an email that looks something like this and this correspondence will have the new number
I wish to inform you that, in accordance with the Access To Information Act*, an extension of xx days beyond the statutory 30 day limit is necessary to process your request. This extension is due to a large number of records or necessitates a search through a large number of records and meeting the original time limit would unreasonably interfere with the operations of the government institution.
Considering the extension, your request is now due on Month, Day, Year
Further information about the Access To Information Act* can be found at the following web page:
http://laws-lois.justice.gc.ca/eng/acts/a-1/
Please be advised that you are entitled to submit a complaint regarding the processing of your request to the Information Commissioner within sixty days of the receipt of this notice. The complaint form can be retrieved at:
http://www.oic-ci.gc.ca/eng/lc-cj-logde-complaint-deposer-plainte.aspx.
Should you have any questions, please do not hesitate to contact us by email at
IRCC.ATIP-AIPRP.IRCC@cic.gc.ca.
Sincerely,
ATIP Officer
Immigration, Refugees and Citizenship Canada