In order to work in Canada as an immigrant you will either need a work permit, or a permanent residence. A work permit is only for a temporary period. You can find out more specific info here:
The rules differ depending the occupations and circumstances. You can find a list of jobs that don't require a work permit here:
If you wish to apply outside Canada you should follow this link:
If you are already a permanent resident of Canada, you can simply apply for a Social Insurance Number (SIN Number). You can apply for a SIN number at Service Canada.