To receive a work visa, a temporary foreign worker would need a sponsorship from an approved employer in Canada. This employer would offer you a written employment offer and a contract. Using this sponsorship, you can apply for a work visa which usually is valid for 2 years or less depending on the contract offered to you by the company. During this tenure, since you receive the visa due to the sponsorship of the particular employer, you are not allowed to change your employer. These visas are usually available to candidates who are in demand in Canada.