You can only apply for a work permit from inside Canada if:

• you have a valid study or work permit, or your spouse or parents have a study or work permit
• you have a work permit for one job but want to apply for a work permit for a different job
• you have a temporary resident permit that is valid for six months or more or
• you are in Canada because you have already applied for permanent residence from inside Canada. You will have to pass certain stages in the main application process before you can be eligible for a work permit.

You must also have the following documents:

• a job offer from a Canadian employer
• a completed application, that shows that you meet the requirements of the Immigration and Refugee Protection Act and the Immigration and Refugee Protection Regulations, and
• written confirmation from HRSDC that the employer can hire a foreign worker to fill the job. This confirmation is called a positive labour market opinion

-In most cases, it is up to your employer to get that written confirmation. Information on the labour market opinion is found under Information for Canadian employers on the right-hand side of this page.

-In some cases, you do not need a labour market opinion. (See Jobs that require a work permit but no labour market opinion.)

You must also do the following:

• Satisfy an immigration officer that you will leave Canada at the end of your work permit.
• Show that you have enough money to support yourself and your family while you are in Canada.
• Respect the law and have no criminal record. (You may have to provide a police clearance certificate. See Have a medical exam or criminal check done in the I Need To… section on the right-hand side of the page.)
• Show that you are not a risk to the security of Canada.
• Be in good health. (You may have to have a medical examination.)

Note: if you are a temporary foreign worker in Canada who has a work permit under the Pilot Project for Occupations Requiring Lower Levels of Formal Training (NOC C and D), and you want to extend your stay, please see Pilot Project for Occupations Requiring Lower Levels of Formal Training (NOC C and D) in the Related Links at the bottom of this page.

Source: www.cic.gc.ca/English/work/apply-who-eligible.asp#inside