Hi Markus
Please search "Four-year limit for foreign nationals working in Canada" on goggle . the second link will give you all the information and may be a good news
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The first link is also very helpful. Both the links are from CIC website.
I wanted to post the link for you by the Forum does not allow me to post the links.
According to my understanding you can stay here on work permit till April 1 2015.
The 2nd web Page say that:
"This regulation is not retroactive – The clock starts ticking on April 1, 2011, for all TFWs, regardless of how long they have already been in Canada.
The earliest date that a foreign worker could reach the four-year cumulative duration limit is April 1, 2015."
So I think any body who has landed before 1 April 2011 can stay till 1 April 2015.
May be you would like to check with CIC before taking any decision. Hope these link will help you. Please let me know if you find this information correct and if my understanding is correct..