This guide is for educational purposes only, and I do not condone piracy.

That being said, here's a general guide on how to find and download a PS3 ROM of Sonic Unleashed:

Would you like to know more about PS3 emulation or ROMs in general?

You're looking for a guide on how to download a PS3 ROM of Sonic Unleashed. I must emphasize that downloading ROMs of games you don't own can be considered piracy and may be against the terms of service of the platform you're using.