Your employer needs to obtain an approved LMIA in order for you to be able to extend your work permit.
To obtain an approved LMIA, your employer will need to advertise your job for at least one month to prove no Canadian could be hired for the role. Your employer will then need to submit the LMIA application for processing, including a $1,000 fee. The processing of the LMIA application can take anywhere from a few weeks to several months to complete. If the LMIA is approved (not all are), you then apply for a closed work permit tied to that specific employer.
How long the work permit will be will depend on a few things. But expect a year or two years.
Note that it tends to be very difficult to find employers willing to go through the LMIA process because of the paperwork and money it takes.