You are the one who applies for a work permit.
However before you can apply for a work permit, you need to find an employer in Canada who is willing to give you a full time job offer and who is also able to obtain an approved LMIA. The LMIA process is quite long (often 4-6 months) and expensive for the employer - with no guarantee of approval. For this reason, it tends to be extremely difficult to find employers willing to go through the process.