But next week I won't have won the Xanadu prize in the SPSC raffle
Because you have to connect in the States, you do NEED a passport. I saw a Canadian woman trying to get through customs/security in Charlotte NC without one...talk about a gauntlet! She was at the kiosk for at least 20 minutes and then was ushered off to another room for gawd knows what.
Although it could happen anyway, for any number of reasons, I think you're better off jumping through the hoops here rather than appear to be a security risk in the USA just because you don't have a passport.