re: 3 weeks in the USA.

New Orleans, Grand Canyon, Vegas, Los Angeles are obvious.

Some good stops along the way, though, would be:
Scott, LA for some boudin

Austin, TX for some BBQ and live music

San Antonio, TX for the River Walk

Phoenix to bang sluts at Arizona State

Once you make it to California, you could drive the Coast Road up to San Francisco, visit Sequoia, or even go all the way up from San Francisco to Portland, OR and Seattle, WA and end your trip up there.

Obviously, eventually, you'll have to come back to the states to get a tour of the northeast, hitting up DC, Philly, NYC, Boston, and Maine. Or maybe a midwest trip to see Chicago, Detroit, St. Louis, Nashville, and Memphis.