No you can not. In China you would use a chinese network. Therefore you'll be paying roaming charges for using that network. Unlimited international only includes texts sent and received when you're in Canada
Hey Lan! Robert is right, your Koodo plan does not cover usage outside of Canada. Incoming texts will be free; however, outgoing messages will be $0.60/sms in China. More information about rates and add-ons for travelling can be found here -> http://koo.do/trvllng . Let us know if you have more questions!