Greetings
@Arrelety . I cannot offer specific tips since I live in the US. I do know that here it is very difficult to get on disability and I don't know how hard it is there.
But one thing that I feel certain is the same is this: You have to really know what you are doing. Don't just get the forms and fill them out. You need legal advice from someone who knows the whole system and knows how to do things, how to word certain things, and exactly what kinds of evidence you will need to supply.
For instance, here you need to be able to prove that you cannot work at all at any kind of job, and that this has been the case for a certain period of time. If a person is still working, even part time, they will not get approved. You need doctor's reports, medical records, etc.
In the US we have "legal aid", which helps people with legal issues on a sliding scale. If you can't afford an attorney who specializes in disability claims to advise you on this, maybe there's something similar in Canada that you can find and go to them for advice. I also recommend doing a lot of research online about it, specific to Canada, and read people's posts on social media to see what you can learn.
And if you don't succeed at first, you can try again. Here, people have been known to apply 4 or 5 times over as many years before receiving it.
I hope it's not that hard in Canada, where health care is so much better and so much more accessible and affordable than it is here!