This should help:
A temporary foreign worker can work in Canada for a maximum period of four years. Therefore, you need to keep track of the time you work in Canada as of April 1, 2011. However, there are some exceptions to this rule if:
the work you intend to do in Canada creates or maintains significant social, cultural or economic benefits or opportunities for Canadian citizens or permanent residents,
the work you intend to do in Canada relates to an international agreement between Canada and one or more countries (including seasonal agricultural workers),
your work is done while you are authorized to study,
48 months have passed since you accumulated 4 years of work in Canada or since you last worked in Canada.
If you did not work during the entire specified period on your work permit (for example you have a work permit valid for four years and you were sick or you left Canada temporarily), you would need to submit proof of time not worked when you apply for another work permit later on and you are close to the four-year maximum. Examples of proof documents include but are not limited to:
passport entry and exit stamps,
Record of Employment from Service Canada,
receipt of severance pay,
letter from a foreign educational institution where you attended school,
travel receipts (tickets, boarding passes),
proof of receipt of maternity/parental benefits,
letter from physician confirming you were on medical leave,
any other document that demonstrates that you were not working in Canada while on a work permit.
Note: It is your responsibility to keep track all worked performed and of any breaks in work while in Canada on a work permit. You will be required to provide documentary evidence to prove periods where you have not worked in order for that time not to count towards the four-year limit.
