TPear said:
Is it necessary to use representative? or we can apply independently? what is better?
It is not necessary to use a representative. You are free to apply on your own.
Also there is more than one type of representative. There are consultants who promise to help you with your application for a fee, and then there are immigration lawyers who can offer you legal advice as well as help with your application. I chose to engage an immigration lawyer with years of experience and a good track records because I feel more secure doing that. But it certainly is not necessary, and so long as you file a complete and accurate application that meets the requirements you should be just fine.
Note that there are many dishonest or lazy "consultants" who take fees from people and then do a poor job on the application or mislead people into thinking they can help them qualify when they actually don't, or help them obtain documents they need, etc. Don't fall victim to a scam like this! CIC maintains a list of recommended consultants who should be better than one you just find on the internet.
If you like, I can refer you to my attorney.