PDF page content that is solely the scanned image of textual content is not accessible PDF.
A PDF having content that is a scanned image of text (and other content having semantic value in the document) can be made a PDF/UA compliant PDF.
OCR would have to be done. The OCR output would then be corrected (OCR does not provide 100% character recognition accuracy).
This OCR content would then have to have the semantically appropriate PDF elements (tags) provided.
Done properly the PDF becomes PDF/UA-1 compliant.
A PDF/UA-1 compliant PDF will more than satisfiy AODA.
An accessible PDF is an ISO 14289-1:2012 compatible PDF.
ISO 14289-1 (PDF/UA-1) is the ISO standard for accessible PDF.
As with other PDF related ISO standards PDF/UA-1 is based on the ISO standard for PDF (ISO 32000-1).
So to provide an accessible PDF it is good to be familiar with these two ISO standards.
Additional resources are available at the AIIM web site:
Two documents are currently available with a third pending.
--| Achieving WCAG 2.0 with PDF/UA
--| PDF/UA-1 Technical Implementation Guide: Understanding ISO 14289-1 (PDF/UA-1)
--| PDF/UA-1 Technical Implementation Guide: Understanding ISO 32000-1 (PDF 1.7) (under development)
You might also want to check the Web Content Accessibility Guidelines (WCAG) site for help on making documents accessible so they are in compliance with ADA.
There is a lot more to making a document compliant than meets the eye (no pun intended).
Technique specific to scanned documents ...
At first I thought the ‘O’ was a typo. AODA = Accessibility for Ontarians with Disabilities Act, right? The PDF accessibility advice on the AODA site (http://www.aoda.ca/the-four-levels-of-pdf-accessibility/) makes good sense but lacks specifics. I think the previous posters are on track. If you achieve WCAG 2.0 compliance you can have confidence that you are AODA compliant as well. I find the free PDF Accessibility Checker (PAC) from the Swiss foundation Access for All to be a great help in testing for PDF accessibility. The AODA site has a welcome sense of humor, by the way – see http://www.aoda.ca/ontario-government-aoda-implementation-delayed-due-to-sexism/.
In a nutshell WCAG 2.0 for PDF *is* PDF/UA-1 (ISO 14289-1:2012).
In fact PDF/UA-1 goes above and beyond WCAG 2 in a few areas -- like font embedding. Coming from a print background I learned early on that fonts should *always* be embedded for print. But it's likewise for reading on screen... font substitution can make a PDF inaccessible to anyone. I don't understand why this standard wasn't included in WCAG.