Like many mortgage brokers, I get several calls a month wondering if you can get a mortgage if you are on ODSP (the Ontario Disability Support Program). Although this source of income is tax free, most lenders unfortunately do not view it as a permanant source of income, as the pension is income tested and case workers will not put it in writing that the pension will continue to a certain age.
That being said, I have helped families get mortgages in the past where one member was receiving ODSP but there was always a secondary source of income (either a another pension or a spouse/partner with a job). All of these applicants also had good credit and a downpayment/closing costs from their own resources (you will need a minimum of 20% down).
The moral of the story? Try to give a potential lender more reasons to say yes than say no. Keep all your bills up to date and within their credit limits, Start a regular savings plan. And depending on the nature of your disability, do whatever possible to secure a secondary source of income if you are able to do so.