It's a bit early to say. They will sell well, but we need to see the games and Nintendo's approach. People love innovation with Nintendo's games. Super Mario Galaxy was great - it had a neat theme, neat name and fantastic graphics and gameplay. If Super Mario U is revealed for this fall and it is called Super Mario Universe, has spectacular worlds to explore, neat new gameplay twists and fun new multiplayer using the game pad for more than collecting stars - the game will probably be huge, sell 10 million plus and move a bunch of systems so that other games sell well too. If it's Mario Sunshine 2 and releasing in February, it will sell around 7 million and not move as many systems, which will affect everything else.
This carries down the line. Mario Kart should hopefully be a big jump graphically and seem fresh. If it is, it will be a big mover. If it's a bit stale like some people felt NSMBU was (not me) it could see a lesser impact than the Wii version. Zelda, if it's mature and graphically stunning and has fresh gameplay (multiplayer? open world?) it could be massive, upwards of 10 million. If it's toony, then it will be lucky to hit 5 and again, it will negatively impact the systems sales themselves.
As far as the games we already know a bit about, I think Pikmin 3 is going to be the biggest selling Pikmin title. It will come close to 2 million. WWHD is perfect for WiiU, as the early adopters are the kind of people who will gobble it up. They are either people who loved it on GameCube or never played it but would like to now. When it hits it should impact system sales significantly. X should exceed Xenoblade sales by quite a bit. If it turns out as well as the trailer implied, and if Nintendo treats it as a major 1st party title with worldwide launch, it could become a bit of a system seller and sales could be upwards of 3 million.
I'm not too concerned of WiiU sales vs Wii sales, because I look at it in the opposite direction. I don't think it's the install base that makes good software sales, but rather software that will drive up the install base. If the games are good, people will buy Wii U to play them. Especially if it comes down $50 and is the cheapest system.
