Well vita got a boost from Vita TV in Japan and then that dropped like a rock, so in japan, we should see Wii U outselling Vita routinely. In the US, if Black Friday week is any indication, consumers arent really down to buy a Vita. In Europe, even with Wii U doing pretty damn terribly, it is still keeping up with the vita for the most part.
Additionally, Wii U has more system selling software in the pipeline.
Unless Vita catches on as a PS4 accessory or Vita TV is a HUGE hit in the West, I think Wii U should make it to 10 mil first.