There is a Post Graduate Plan, which means you will have to get a job offer within three months since your graduation. If the three months expires, you will have to try some other ways to stay. You could also try to find some job which gets proved by HRDC, without the time limit. But this is even harder to get.
Check this website to get relevant information: http://www.hrdc-drhc.gc.ca/ http://www.cic.gc.ca
Anyway, good luck! If you have more questions, you could contact me by QQH!