From a visitor visa to a work visa, application has to be made outside Canada unless the applicant falls in these categories, then they can apply in Canada:
The following persons may apply for a work permit from within Canada:
•Holders of work or study permits and their family members;
Note:Spouses or common-law partners of highly skilled temporary foreign workers, may themselves be authorized to work without first having a confirmed job offer by Human Resources and Social Development Canada (HRSDC confirmation). In the case of workers destined for Quebec, without having to obtain a CAQ from the Ministère de l’Immigration et des communautés culturelles (MICC). The principal foreign worker must be doing work which is at a level that falls within National Occupational Classification (NOC) Skill Levels O, A or B in order for them to qualify for a work permit. These skill levels include management and professional occupations and technical or skilled tradespersons. For further information on the program and a list of the skill levels in the NOC, refer to our Web site.
8 Applying to Change Conditions or Extend Your Stay in Canada - Worker
•Successful graduates from a program at a Canadian university, community, college, CÉGEP, or publicly funded trade/technical school (or from a Canadian private institution authorized by provincial statute to confer degrees) who wish to work for a maximum of one or two years in employment related to their course of study. The maximum length will depend on the length and location of their studies, and the location of their employer. Graduates must submit an application for a work permit within 90 days of the issuance of your final marks. Their study permit must be valid upon submission of their application for a work permit. For further details refer to the Foreign Workers Manual (see post-graduation employment) located on our Web site or contact the Call Centre listed under the Contact Information section;
•Persons who don’t require a work permit who are applying for secondary employment in Canada, who have been working for at least three consecutive months in Canada and are not business visitors. Family members of these persons may apply before three months have passed if they satisfy an officer that the principal worker will work for at least three months;
•Holders of temporary resident permits (TRPs) valid for a minimum of 6 months and their family members;
•Refugee claimants and persons subject to an unenforceable removal order;
•In-Canada permanent resident applicants and their family members who are members of the following classes, determined eligible for permanent resident (PR) status:
live-in-caregiver, spouse or common-law partner, protected persons, and humanitarian and compassionate considerations (H&C);
•Persons whose work permits were authorized by a visa office abroad, where the permit was not issued at a port of entry;
•Mexican citizens who have been admitted to Canada as visitors may apply for a work permit under any North American Free Trade Agreement (NAFTA) category. U.S. citizens admitted as visitors may apply in Canada under the Professional or Intra-company Transferee NAFTA categories only. These provisions are in accordance with reciprocal arrangements.
http://www.cic.gc.ca/english/pdf/kits/guides/5553E.PDF pp7-8
