ATIP and GCMS
Short definitions. Official expansion, then the Canada.ca page.
ATIP is the shorthand federal institutions use for work under two statutes: the Access to Information Act and the Privacy Act. There is no federal law called the Access to Information Privacy Act. IRCC says a Canadian citizen, permanent resident, or an individual or corporation present in Canada can make a direct Access to Information Act request, and the application fee is $5. The Privacy Act is for your own personal information. IRCC says Canadian citizens, permanent residents and foreign nationals can use it regardless of location, and it is free. Eligibility, fees, and complaint routes differ, so you need the correct Act when you request and when you complain.
I would start with the reading guide if you already have notes. I would start with the request guide if you still need the file. Official request doors stay on IRCC's access to information and privacy page.
How to read GCMS notes. Start with the refusal letter, then the officer notes beside it.
How to request GCMS notes. Choose the Act, file the request, and keep the receipt.
A local-browser docket for a late Access Act request. It is not IRCC and it is not Unredacted.
Short definitions. Official expansion, then the Canada.ca page.