As a rule, only people with a valid work permit or an unlimited visa can work in Canada.
For a regular work permit, the employer must first obtain permission to hire a foreign national from the government by means of a relatively difficult process. The Canadian employer must demonstrate that they cannot find a Canadian who can or will do a specific job. Only after this permission is acquired may a foreign national be hired if his or her professional experience and education exactly match the advertised job in Canada. If these conditions are met, obtaining a work visa is fairly easy, although it should be noted that such visas are generally limited to 1 – 4 years.
Canada has international treaties with other countries such as Germany, Switzerland, and Austria that make it much easier for younger people under 35 years old to obtain a work visa to try out the job market in Canada for 6 months to 2 years. It should be noted that the exact requirements vary depending on the country you are coming from.