As far as Accept/Cancel bindings, the PS3 usually piggybacks on whatever your hardware was designed for. So, when you plug in a Japanese game into an American PS3, Cancel is O and Accept is X. If you plug an American game into a Japanese PS3, it's the other way around.
Based on what I'm hearing, it could be that the demo controls only takes the system's cancel button, and for some reason sets its own accept button to Circle. Which means, short of changing your hardware (i.e. buying another PS3), there's no way to get around this. This also makes me curious to know if there's button configuration in G4U (since... I guess I can't think of any other place it could be coming from, except for plain hardcoding).
I don't think changing language should have any effect, but since it's really simple to do, you can still try it.