When was there a switch? Sakura was never going to pair up with Naruto from the get-go, because she was adamantly in love with Sasuke. On the same token, Hinata was adamantly in love with Naruto. Naruto was the only variable here, who could decide either way.

I say the canon pairing was officially locked at the Hokage Summit arc where Naruto was fed up with Sakura's lies (took him a while but Naruto wasn't the sharpest kunai in the satchel).