The clean guitar patches on all synth modules I've heard are almost always Fender Stratocaster samples. It was like I originally said, guitar samples will generally fall into the Fender or Gibson categories. Even if another guitar is used it will have either that single pole or humbucker sound.

I'm very sure that you can find a sample set that has Fender Strat sounds. In fact most guitar sample collections are bound to include some variations of the Fender Stratocaster. That will give you very much the same sound as the Roland clean guitar sounds.