Hi and welcome to the forum.

The matter of hiring an agency to handle your visa depends on what sort of visa you're looking for and just what obstacles you have to clear. Have you studied the Immigration Canada pages? Welcome Page | Page d'accueil

I would be wary of "promises" made by any agent for immigration. If you don't qualify under Canada's point system, then you'll need to find a job to get work sponsorship. If the agency is promising to find you a job in Canada, I'd be a little skeptical. They can promise to do their best, but it isn't always possible to promise a specific result when it comes to immigration. An agent can handle the paperwork for you (which can be pretty daunting) and can save you some considerable running around and waiting in line.
Cheers,
Bev