The Connie's size according to one one definition of canon is still 289 meters long, because it appeared on a screen in Discovery Season 1, and a barely readable screen in TOS.
If you believe that things written on screens shouldn't always be canon, than the Connie doesn't have canon length.
The size of almost every ship in Star Trek isn't canon, a majority of ships aren't given sizes on screen, they come from BTS materials.
Everything on screen is canon, whether I can read it or not. But if someone on screen actually states that the Enterprise is larger than 289 meters, then that trumps a barely readable screen.