Hey
After finishing one year studies, you will get one year PGWP. This will be a open work permit. That means you will get it for sure whether you have job or not. This is the time where you should push yourself to get a decent job. If you get a job in your field, you employer has to file LMO (labour market opinion) with service canada. After your employer get positive LMO, then you can apply for a new employer specific work permit. There is no way that you can extend you PGWP. PGWP can't be extended. It can only be changed to employer specific work permit. Please follow the link on CIC website"Hire temporary foreign worker". There are some exceptions to LMO rule which you have to find out by visiting CIC website thoroughly.
Hope this helps.
Yaju