Danito, you're gonna have a great time.
I have never been to Seattle, so can't say, but San Francisco, you'll love. There's a lot of touristy things to see like the Golden Gate, Alcatraz, Lombard St., Fisherman's Wharf, and riding the cable cars a lot of fun as is walking thru Union Square. Oh, lots of nice restaurants too.
NYC, what can I say, that is sensational, one of a kind and a must see; someplace you'll never forget.
I'd suggest checking tourist sites and get an idea on each city of what you want to see most. Speaking for the two cities anyway, I'm sure you'll find lots to do.
Have a wonderful time.
TIS