To maximize your chances of getting a job in Canada, you should ensure that you have a positive image with recruiters. Whether or not that job offer is valid depends on whether or not your future employer can obtain a positive evaluation of the impact on the labor market (LMIA, formerly LMO). An LMIA is a permit from the Canadian Ministry of Employment and Social Development to hire a foreign worker for a job for which no Canadian citizen or permanent resident can be found. A job offer from a Canadian employer can significantly increase your chances of receiving an invitation to apply for permanent residence.
A good way to make sure you don't fall on the wrong side of recruiters is to be selective with the jobs you apply for. However, you might prefer to try Indeed instead (again, the Canadian site), as it collects job offers from Monster, Workopolis, and many other job sites, meaning you only have to search in one place. Your country may differ in terms of labor market, application processes, the most in-demand occupations, and even job titles. Many employers use LinkedIn as a way to research potential clients, so it would be a great help for any job application of yours that is supported by a LinkedIn profile.
You can visit their websites to get an idea of the company's culture and to learn about job offers. While this increases your chances of receiving a visa to Canada, not having a job offer won't block your ability to move to Canada. First of all, you should know that it's illegal to ask someone to pay for a Canadian job or for a job offer letter. Job Bank has long been the way Canadians find work online, as it's free for both employers and candidates.
Now that you have a good idea of how to get a job offer in Canada, it's time to start with the application process. If you can't find a job offer, you can try to get accepted to a Canadian university, but that's extremely expensive even if you qualify. Asking previous employers in your home country to provide you with references can go a long way in getting a job in Canada.