Hey Tsooma
Let's start from the beginning.
You have mentioned that you didn't receive any additional request from CIC.
1. do you know if your application is routine or not?
according to CIC, to fall under non-routine one, you should have received rq, fp or just request for additional documents, also if you tried to change your name, DOB or anything else in the application. That's official story, however, case officer can deem your application as non routine without following official guidelines. As my lawyer told me, 36 months still IS unwritten deadline for non-routine ones. That part was eliminated from IRCC's website but Fed Court still follows this rule.
2. To apply for mandamus, you should have tried every possible way to resolve the problem with IRCC; that includes your MP's involvement and communication with McCallum (his aids) through your MP or directly.
3. Have you received any reply on your Case specific inquiry ?
4. Demand letter has more weight if it's done by your representative (attorney), but he/she might ask you to fulfil the option 2 first (MP and McCallum).
5. File going back and forth doesn't constitute any actual 'action' on your file, (tip from my lawyer, as my file changed hands and shelves quite a few time in St.Clair office).
6. Application for mandamus after your demand letter has few stages;
1. Application for leave - application to federal court, same time IRCC and Department of Justice are served.
2. DOJ has to reply in 10 days if they will represent IRCC in court (they will).
3. Request for information regarding decision on your file from IRCC (done by court or DOJ), IRCC will reply that application has no decision.
4. After IRCC's reply, your lawyer has 30 days to prepare and file the argument to the court (more detailed one).
5. DOJ has to come up and share information before the court, why there was a delay. If DOJ lawyer sees that application is delayed unjust, she/he will try to persuade case officer to finish the application.
I have no idea regarding next stages yet.
But as you can see, 36 months still is 'unreasonable' delay if application is Non-routine.
If I were you, I would take this information with a grain of salt, I'm sharing what I know but some people might have more detailed experience.