Do the Standford University Summer College, it's a much better experience. I did it this past summer and had an awesome time. There were quite a few international students in the program. You enroll in their summer undergraduate courses with Stanford students (the CS class I took even had graduate students in it) and get actual college credit for the classes. I'm not really familiar with EPGY or CTY, and Junior Statesman is a ripoff for the little you get out of it.
The programs won't guarantee your admissions in the university but I'm sure they can't hurt and the admissions people at least can see that you have a lot of interest in the school.
Stanford Summer College:
http://summer.stanford.edu/
Do it, I guarantee you'll have an awesome time.