We have had a little experience with the disability tax credit (Canada). Keep in mind this is completely separate than getting a disability pension from the federal government, because that is an entirely different qualification process.
The bad news is, the government has drastically tightened up eligibility requirements for the tax credit in the last few years. You have to pretty much unable to get out of bed or function at all to get it. I would advise that if you are going to apply for it, make sure the doctor is familiar with the process and knows how to check the right boxes.
My spouse originally qualified for it back from 2005, but they wouldn't renew it in 2010 and turned down our appeal. Our doctor told us that pretty much all of her patients and those of other doctors were getting rejected. This is despite my wife's disability that leaves her unable to work and costs over $10,000 a year in medical costs - thankfully we have decent insurance through my employer.
The loss of the disability tax credit costs my family a good $2,000 off of our tax return. When the Conservative Party called me for a political contribution, I told them to take it of the tax credit they pulled out from under us.