My visa is expiring in six months so I am thinking to go to canada to extend it ? Does anyone have this experience of going to canada to extend visa. Can you tell me whats the process and the risks or chances.

I would really appreciate your help.

You can apply for student visa once again like you did before. there is no risk. just say that you may need to visit outside the US in the future so you need visa...etc. I am sure they will issue a visa. AND, you will not need to surrender your I-94 while going to Canada for less than 30 days, so there is no any point of risk associated with this. But Never forget to have your I-20 signed from your school's intl. office. Its kinda authorized travel signature.
best of luck!

...because I did the same thing not from Canada but from Nepal during this vacation and got new visa. Its no extension, you'll get a new one and your old one will be "cancelled without prejudice".

If you did not already know, you do not need to extend visa unless you plan to go abroad. As long as your I-20 is valid, you can continue to stay in US and maintain your status. So, you can easily renew the visa when you go to Nepal. You need it when you plan to come back to USA.

No you cannot get  F1 visa from canada you will have to get it from Nepal. and yes like others said you dont need to have visa unless u plan to go out of US.

good luck