Sony has announced that the upcoming Blu-ray release of the God of War Collection, which includes the original two games, will also have a code for the third's demo.
That's four months before the game goes on sale in the shops, presuming the God of War III demo is ready on or around the retailing of the Blu-ray compilation. I and II remastered in 720p.
This November the God of War Collection will go on sale in the U.S. for $40, and it has been revealed as region free so imports are a likely scenario but the code for the demo is likely to be locked for the US PlayStation Store. Check out the E3 stage floor footage for God of War III.