Syaoran was a 9 years old when he met Sakura, Touya even said to Yukito he didn't care about that almost fight and when Sakura said "Syaoran-kun always help me" Touya said "That's why I don't like him". In episode 67 Yukito also defended Syaoran saying he is a good boy and Touya was like "yeah but he will take someone [Sakura] away"
True! When Yukito asked him why he hated Syaoran so much, if it was for what he did to Sakura the first day he came, Touya said that it wasn’t for that, that it was nothing from the past, it was for what is going to happen.
So this makes me think he knew this for a loong time 🤔