if you have a visitor visa only you are working illegally and are at risk of being deported (and prevented from ever returning to Canada).
If you are on a work permit, you permit will stipulate for whom you are permitted to work, and where you are permitted to work. If it is an open permit changing jobs should not be a problem.
If not, and you wish to change jobs, step one is to find an employer that would be willing get an LMO, which will allow you to apply for a new work permit, for the new job. There are several rules about this, so have a look at the CIC website for clarification.
If you are able to obtain family sponsorship, or perhaps qualify for permanent residence in some other way, I would suggest you apply for that, as once you have PR you can work in any job anywhere in Canada.
Good luck