your school will issue you new I-20 when you file for graduation, if you have already filed then you should consult with your International dept for new I-20 which will be until the period for your OPT, but if you haven't filed for OPT then you would not be issued new I-20, in that case you have 45 or 60 days to leave country.

Once you recieve new I-20, i think you could visist canada, since your I-94 says visa until school is finished. But since your new I-20 will have date till next year you should be fine.

Consult with your Intl' dept anyway, just for peace of mind.