Depends on what we're talking about.........
UFC style fighting would result in something ugly for both Lee and Segal. I've always maintained that grappling would go to Norris every time.
Segal's problem is that he's mastered "aikido". This art is much different from the rest. In fact, what you see in his films is rather contrary to his art. Aikido is very much defensive only. In its truest form there is literally no "offense" in aikido, except to defend. In many cases it's the offense of the offender that is turned against him. In other cases, the defense is initiated by the person attacked, but holds are boring so Segal's movies have always focused on "finishes" (which Aikido is also good at).
As for Bruce Lee's blend of mastery in various martial arts, I'd have to say that between the two, I'd have to give it to Bruce for points, if we're talking about a points fight. I think he'd be simply too fast for the other two.
As for knockout style fighting without lethal or bone-breaking moves, I'd have to give it to Chuck Norris. In this case, Segal would be a non-factor.
So, I see three possible winners among three styles of match. As much as I'd love to give an answer, I honestly couldn't pick between Lee & Norris. It's anybody's guess. For Segal................if he missed either man's offense, then he'd be left with no defense. One missed move and it'd be over. Easy to catch & execute every single offense/defense in a choreographed movie, not so in real life.