You need to get a single certificate notarized by the Chinese consulate. You need your divorce papers, single declaration and current marital status notarized. Then send it to the Chinese consulate for a single certificate or go in person. You need your single certificate to be translated also which can be done in China. The single certificate is only good for 6 months.
To start the immigration process you need to be married first. You don''t need a lawyer to help you with the immigration application. They just check to see if everything is filled out correctly and have the supporting documents. A waste of money if you ask me. Just take your time with the application. All the documents you need for the application will be on Canada's immigration website.
Before you get married keep all phone receipts, email, phone logs and even chat logs even if you chat by webcam it will log it as receiving or answering a call on the log. Keep all travel records (plane tickets stub, hotel receipts, etc) including any gift receipt you purchase for her in China. On your next trip to China when you marry her bring the immigration paper work with you so you can help her fill them out in China as she need to sign off on some documents. Print off extra copies in case. Also make sure your wife get a medical examination to be submitted along with the immigration application, You can check on the Canadian immigration website on where it the authorize area that can do the medical examination. That way you do not have to send her the documents and then wait for them to be mailed back to you.