Could make a case for Legends Sidious winning imho. He's not going to toy around with these three like he typically does - Vader is susceptible to lightning, we already know he can ramp it up and move faster than Maul can perceive/react to, and he can choke Tyranus from lightyears away.
I don't see why he couldn't just crush a windpipe or two right off the bat.
Round 1. Team wins. Dooku and Vader together are enough to pressure and even beat Sidious.
Round 2. Sidious has some pretty good feats for Legends. However team also gets there's so hard to call. He would need to get rid of maul quickly and then take out Dooku or,Vader and the lone survivor can't take Sidious.