I applied by myself first. But due to unknown reason, I didn't hear anything from Embassy at tall. So I decided to hire Maple International to relook at my case. So far, they have good customer service.
I regreted not hiring them in the beginning. Otherwise, i would have landed in Canada already.
Always hear Chinese say it is not worth to hire a lawyer. Now I think this is a big thing in your life, and they only charge you very small compare to US immigration. It is not really worth it to save a litte bit money and risk your chance.