Canonical has put up a timer on Ubuntu's website with the text "Tick, tock, tablet time!" We widely expect this announcement to be a tablet-optimized Ubuntu operating system as Canonical isn't known for making hardware and we have no reason to believe they are going to get into the hardware game.
It's not clear whether the tablet version of Ubuntu would be based off of the desktop version or off of the new smartphone version. Either way, Canonical needs to establish itself across the entire mobile stack in order to make itself a viable mobile operating system.
Canonical has already confirmed plans to launch a tablet version of Ubuntu. We'll have to wait another 18 hours or so to find out the full details. We'll be sure to have coverage of the announcement along with coverage of HTC's press conference scheduled tomorrow.