OHIP has been clamping down on some tests over the past few years that they think have been over-prescribed. B12 tests might be one of them. The current rules for PSA tests can be found here:
When and where to get screened for prostate cancer.
www.ontario.ca
OHIP will pay if the doctor SUSPECTS you have prostate cancer. Otherwise you will pay, even if the doctor checks the PSA box on the requisition along with other covered bloodwork.
If you're covered by OHIP and you've had PSA tests that you haven't paid for, it's because your doctor genuinely suspects you have prostate cancer - or he fraudulently claimed that on the form just so you didn't have to pay for it. It's $35 if you pay for it.