Can you still apply for co-ops/internships after you graduate?

Not sure about internships, but not co-op positions through the school.
One of the co-op requirements for the school to provide an accredited co-op program is that you return to studies for your last semester before graduation (your last term can't be a work term). So if you've already graduated, that ship has sailed.

^This

And on top of that I think I read somewhere companies would not receive some sort of tax credit(?) if they hire a graduate for coop position