According to GameStop, Sonic Unleashed will be coming to the Wii, PS2, Xbox 360, and PS3 on November 4th, 2008. The prices vary from SKU to SKU, but the PS2 version will be selling for the budget price of $30, while the Wii and PS3/360 versions will be going for the standard $50/$60 price tag respectivey.
GameStop can often be a source for new info on upcoming games, with prices, release dates, names, and platforms for upcoming games often leaked months before the publisher officially announces the info. They where the ones who leaked Samba De Amigo Wii early, among other games. While their track record is very solid, any info from them should still be regarded as speculation and rumor, until officially confirmed by SEGA.