I am not sure of your question, but at least let me get more information from you that may help other help you. Number one, I think the right DAW/sequencer would be what you want, (like
an Ableton Live) but there might be other options. So, let's make sure we have all of the information.
What is your objective? Live playing and it keeps the tempo to your timing? Also, since it has more sounds than just drums, I have to assume you want to figure out how to get it to follow you with the synth part when you play chords/notes?
Without some sort of sequencer/DAW, you want your guitar to be the MIDI input and do two things, tempo and synthesizer duties. Is this correct?
Going straight to the machine, using some sort of sound to MIDI pick up would be required. Now, the main question, has anyone used one of these and which one works the best.
I've seen some on the market, but decided to go a different route (a controller, MIDI keyboard and Ableton) the way Ableton is designed is for use in a live setting (non-linear) and recording normal (linear). But it requires someone manning the software. They do make foot controllers (you would have to look at Ableton to understand why if is different as it works with clips and scenes) for it, not sure how well they work. The software does allow for a very flexible and free flow of playing live. and can drive your Roland (MIDI Out).
But I think that scenario becomes more complex than you want. So Guitar ->MIDI pickup->Roland->Mixer.
I know, lot of words, but here is a start:
MIDI Converter you can read the reviews. Price is not bad if it works.