Pretty nice looking exhibit. When it first opened, the female polar bear for the exhibit came from my zoo (Reid Park Zoo, Tucson, USA) and the male came from a zoo in China (I'm pretty sure).
It is indeed a nice exhibit with some sand, grass and deep pool. When I was there, they had four bears, using the exhibit on a rotating basis. Not sure when the exhibit opened first with regards to the bears you mentioned (including the one from your home zoo in Tucson) but the following I wrote down from the exhibit label:
"Hudson and Nelson are orphaned twins born on 15th December 2003. They were cared for by Quebec Zoo until they went to Australia in November 2004. Liya and Lutik are second generation zoo-born twins from Leningrad Zoo in Russia. They were born on 9th December 2000 and have been in Australia since November 2001."
I remember seeing on Animal Planet a show about the transport of the twins from Russia to Australia. I assume the bears you mentioned (from Arizona and China) preceded these four?