Physically, he is stronger than both but would inevitably lose this match-up. Not maintaining eye contact, he gets roasted with Amaterasu and if he does make eye contact then he's caught in Genjutsu and finished off. Madara summons the Kyūbi and Guy is yet again finished. While in character, utilizing the Shimon is a last resort and it is only then he would possess power capable of besting Madara's defenses and potentially bypassing Itachi's, but naturally, he would be killed long before then.