If your application is comprehensive security screening, then 60 days extension is normal. For security screening see
If you received an extension, requesting another GCMS notes from IRCC won't help. Instead, just wait it out and too you will have your GCMS notes from CBSA.
The time limits and extensions are sought pursuant to the ATIP manual, see
https://www.canada.ca/en/treasury-board-secretariat/services/access-information-privacy/access-information/access-information-manual.html#cha7
Also, some people have been peddling misinformation that IRCC is arbitrarily taking extensions or more for some and less when they request, which is a bunch of bunch of baloney.
Requesting GCMS notes from IRCC, CBSA or CSIS is a legal process, just like your application processing. It is done pursuant to Access to Information Act and in accordance with the ATIP manual, and each year, all federal agencies have to publish their reports on how well they performed, which is tabled in the Parliament.
As per the ATIP manual, no matter who files the request, it has to be processed without regard to the requestor identity.
Another lies being spread is that filing a complaint with the Office of the Information Commissioner leads to further delays, as IRCC will not release your notes. Filing a comment is your right under the law. Whether you exercise it or not, is your choice.
If you do, then all complaints are looked into and investigated in accordance with the law, which is listed in detail on the OIC website at
https://www.oic-ci.gc.ca/en/how-we-investigate
Unfortunately, some/one person have a poor understanding of law, and this happens. Read the source law, and not someone's vivid imagination of what the law should be as per them.