You don't need any agent. Goto:www.canada.org.cn(Beijing or Hongkong), find visa->returning residence, download the form to fill in and pay 75$ with supporting documents. You can refer to the website for details. In Beijing ,it will take about 6-8 weeks(In the website it said it only take 2 weeks). Remember, you must mail your oringinal passsport and visa with the application form.