Hi Mahmudur,
The process has changed significantly over the last couple of years. It can take you almost 9 to 10 years to be eligible to apply for citizenship. The process goes you first come to Canada on a Work Permit to find and work, after you fulfill all requirements you can take one of the available streams to apply for Permanent Residence (PR) card, once you are PR you will then need to wait with the new laws about 4 years and only when you meet the new requirements in full can you apply for citizenship.
I would advice you to follow this website and links which gives you a breakdown and explains steps required in detail, this is the official CIC website.
http://www.cic.gc.ca/englisH/immigrate/index.asp