I am postdoc form University of Toronto, with T4A (applied at Feb 2013, my status is still "Application Received").
I know some postdocs from UofT who were accepted, and some postdocs who were rejected basing on T4A (in general, T4A is for self-employment and scholarships). This is because some immigration officer do not know about our situation and made wrong decisions.
There are different definitions of employee. According to work definition (not taxation!), postdocs are employee, since: (1) we work full-time, (2) we use University equipment, (3) we are forbidden to work outside the University. Therefore, postdocs are eligible for CEC program. I wrote something like this in my cover letter, and I ask my referees to write it for me. I also wrote that many other Canadian universities had already switched to T4 taxation policies. (I can send an example if someone is interested).
If you are planning to include your contract to your application, read it carefully before doing this, may be it has something that can look suspicious for immigration officer (if you have T4A). And this is not mandatory to include your contract.
You can also write that Ontario Labour Relations Board determined that postdoctoral fellows should be considered as full-time employees within the meaning of the Labour Relations Act. You can ask for more details CUPE