There's no law against merely looking for work in Canada on a visitor visa, but of course you can't work without the proper status. There are 2 main ways of being legally able to work in Canada.
1) If the employer can satisfy Human Resources and Skills Development Canada that there are no suitable, available Canadians to do the job and that they have made all reasonable efforts to get a Canadian and failed, a foreign worker can can be hired and must apply for a work permit. The worker is limited to working for the named employer and cannot even, for instance, rent out a room in his/her house for extra money. It is relatively simple to get a work permit assuming the employer has the "labour market opinion" from HRSDC. Mine took 2 weeks from application to approval in 2004, while the London High Commission's website states 6 weeks on average.
2) If an applicant scores 67 points of more on the criteria set by Citizenship and Immigrations Canada, he/she can apply for permanent residence in the Skilled Worker catagory. The points required are subject to change at any time and it's rumoured that an increase is imminent. To reach a respectable score without an offer of employment from a Canadian employer, you pretty much need to have spent 14+ years in full-time education, be fluent in one official language and have some facility in the other, and have been in the same profession for 4 years or more. Arranged employment makes it considerably easier to reach the points total, but you need an employer who is willing to wait for you! It takes 3 years or more for an application as a skilled worker to be approved for a Brit. There are provincial nominee schemes which speed things up, to maybe a year, and you'd need to check the websites to see how that could work out.
www.cic.gc.ca for the main info
google [name of province] provincial nominee scheme and see what comes up! Probably a good idea to do so on google.ca