about single entry

[yifei8766]

I have a problem about my visa.
I am a visitor from China with a single entry visa.
Can I travel to the US from Canada and go back to Canada by air?
If it is permitted, can I travel for only one time or several times?
Thanks.

 

[dotmatrix]

http://www.cic.gc.ca/english/helpcentre/answer.asp?q=527&t=15