Work Permit
Many people are surprised to find out that they cannot obtain a work permit after they've already entered Canada. This is premised on the basic immigration principle that almost all immigration applications must be submitted outside of Canada, in your home country. Therefore, except for a few exceptions, you cannot chance your status while in Canada. That is, you cannot go from being a visitor to a worker or from being a worker to a student.

Work permits are such a complicated subsection of immigration law that few people attempt to obtain one without the help of a lawyer. In fact, there are law firms who only handle work permits. There are good reasons for this. Obtaining a work permit is usually a two-step process. First, your employer, who has offered you a job offer, must apply to Service Canada for a positive Labour Market Opinion (LMO). If successful, you use that LMO to apply for a work permit in the visa office in your home country.

There are exceptions to this process. Some types of work are exempt from having to obtain an LMO. You can check whether you would qualify here. Also, some types of work do not even require a work permit. You can check the list to see if you qualify. Don't forget that even if you are exempt from obtaining a work permit, you might still need a TRV to enter Canada.

If you wish to obtain a job offer to assist your application for permanent residence in Canada, then, the process is quite different. Your potential employer needs to apply to Service Canada for an Arranged Employment Offer, based on a job offer. You then take that AEO and submit it along with your application for permanent residence. This will give you additional points and fast track your application. You will find additional information here.