Sadly, Haytham probably would notice if Connor were to use Eagle Vision. Not that Connor would really care. He thinks that telling everyone would only help them since they'd have more allies. And he wants Charles to himself so he'd probably be happy if Haytham caught Charles with him.

.... I think I may just have to go with a Charles sandwich OP. I have to admit, Haytham/Chares is my AC3 OTP and the thought of them breaking up breaks my heart. Now adding Connor to the mix... That's not so heartbreaking ;)