You cannot "convert" a visitor visa to a work permit. To qualify to apply for a work permit, you must first secure a full time job offer with an employer in Canada. Your employer must then apply for and obtain an approved LMIA. Once you have the job offer and approved LMIA, you can then apply for a closed work permit tied to that specific employer. It tends to be very difficult to find employers willing to go through the LMIA process.
