Employment Agencies
The are all kinds of Employment Agencies, specializeing in all kinds of fields. They offer temporary and permanent positions to companies that require help in finding staff. These positions might be office personnel, general labourers, skilled labourers, health service personnel, professional and management personnel.

If you are a top executive, or a highly specialized professional in a field where there is a shortage of labour, you might find it worthwhile to contact a Staffing or Recruitment Agency before you immigrate.
However, for most people who like to immigrate to Canada, it will be unlikely that they will get a job offer through an Agency. It is much better to wait till after your arrival in Canada. Companies will not hire people untill they are immigrated and live in Canada.
Know what field you like to work in and contact one of the Agencies specializing in your field.