Wow, that is so cool! What a great friend! If you really like gambling and shows, then Las Vegas is a good spot, especially if you have a lot of money to throw around. Basically, if you've got the money there is a way to spend it there.

I was in Las Vegas for someone's wedding (they lived there, and had a very un-Vegas type wedding) and I found the casinos to be bit tiring after a while. I don't care about gambling that much and I didn't have a ton of money, so I couldn't spend $100+ to see something like Cirque de Soleil. That's just me though. I've been to the Grand Canyon, too, and I think it is just amazing! It's about 300 miles from Vegas so if you did decide to go there you could see both maybe.

My favorite city in the US is San Francisco! It's near redwoods and Yosemite, the ocean, and it's a nice city with a ton of things to do. Sorry to write a book here, good luck on deciding where to go. I'm sure you'll have fun no matter where you go!