is it possible to convert visitor visa to work permit as various agents says its very easy
It's next to impossible. Agents say it's very easy because they either want your money or are scamming you.
To apply for a work permit you need a full time job offer from a Canadian employer. Your employer also needs to obtain an approved LMIA. This is a long (many month) and very expensive process for the employer with no guarantee of approval. As a first step, the employer has to advertise the job in a number of locations for at least a month to prove no Canadian could be found for the role. Generally speaking, it's extremely difficult to find employers willing to go through the LMIA process.
Any agent that tells you this is easy either has absolutely no idea what he's taking about or is a fraud who is going to steal your money.