First you have to find an employer in Canada who is willing to offer you a job.
Next that employer must submit a Labour Market Opinion for approval. As part of this process, the employer must prove that a Canadian could not be found to do the job.
If the Labour Market Opinion is approved, you can then apply for a work permit.
Instructions on how to apply for a work permit are here:
http://www.cic.gc.ca/english/work/apply-how.asp
