Alex O'Loughlin. When in character as Steve McGarrett, he sounds just like an American; when out of character (such as when being interviewed or doing promotional appearances) his Australian accent is unmistakable. Yet again, Steve's American accent is almost too pretty to be real.
Also, Korean-Canadian Grace Park as Kono. But do know that Grace also has American citizenship, since the Canadian government does allow dual citizenship. So it may not be totally true.
Tony Curran as a Boston-born Irish mob hitman in "Ike Maka".
Fake Brit: Australian actress Clare van der Boom as Danny's British-born ex-wife Rachel.
The art dealer in "Mana'o" is played by Bronson Pinchot, who previously played Balki Bartokomous in Perfect Strangers. And played art dealer/weapons dealer "Serge" in the Beverly Hills Cop series of movies.
Branscombe Richmond, who plays the pirate Saloni in the episode "Powa Maka Moana," well known as Bobby Sixkiller from Renegade.
What Could Have Been: Reportedly James McArthur (the original show's Danny) was set to play Danny's father in the remake when he unexpectedly died. The role was actually Mamo Kahike, which was eventually played by Al Harrington (making him the first regular from the original show to appear).