If they refuse, you can ask your manager to talk with HR about the situation, and reassure them that the process will take at least a year. You can then go to your HR department and see if they are willing to provide you with the letter with the required information. You could, a few weeks or months after this, tell them that you are considering it more seriously and that you might need their recommendation, and see if this is something they are open to. You could begin talking with your manager about his thoughts on moving abroad, what they think about it, if they have experience and/or advise on the matter.
You first need to establish confidence with your manager, and not come out of the blue asking for this detailed letter. As long as you provide other supporting documents, and a Letter of Explanation (LoE) detailing why you could not provide the document per IRCC requirements, your application could be accepted.
You have to know that IRCC is open-minded and that failure to provide the letter in the exact required format does not mean your application will be rejected.