Publisher EA previously announced that the PlayStation 3 and Xbox 360 editions would arrive in North America on November 20, with the PlayStation 2 version following on December 18. The November 20 launch of Rock Band in the United States is not affected by this news.
No reason for the delay was provided, though a Harmonix representative previously told bits bytes pixels & sprites that need for bilingual documentation in Canada could slightly delay the game. Conspiracy theorists, meanwhile, speculate the delay may result from EA's anticipated problems meeting the Rock Band demand.
Can they order it from a US site and have it shipped to them?
Probably not from any of the major players. Amazon has a lot of listings that say "for shipment in US only" when it comes to video games.