F1 visa renew in Canada or Mexico?

I've hear Chinese students went to Canada or Mexico to renew visa so they could go back to China and come back to USA with valide visa and without going to America embassies in China.

I want to go back China to visit but my F1 visa had already expired. I was wondering how does the renewing work. Any number I shall call or any angent I shall ask for help?

Thanks!