For marketing I'd push amiibo *hard* on the kids networks along with maybe a Smash CGI commercial.
But for general ads ... I think you might as well take some chances now and try to be different. I'd do something wacky like something in between the Madden Season commercial and wacky Japanese TV ads. The more over the top and fun the better. Fill it up with celebrity cameos.
I'd also maybe take a page out of Sega's 90s style marketing and maybe have some commercials that poke fun at Sony/MS ... ie: a group of obese "comic book" nerd types are lined up for the new Call of Duty or Destiny for PS4/XB1 when they notice Bayonetta 2 on the display and can't believe how crazy/fast/awesome it is and how dull/generic FPS no.238383 looks to them, and then maybe have the hot girl walk in and buy Bayo 2 and shake her head at the guys lined up for COD/Destiny.
Have some fun with it. I'd purposely make the marketing really fun and over the top because I think that angle "works" better for the Wii U and maybe position it as a wacky Japanese product that's "cool" for Americans "in the know".
You can't market "hardcore" head on with Sony/MS, you will lose, but lets take the piss out of the all the "video games are serious business" stuff and position Wii U as the "remember when gaming was just fun?" type thing. I'd purposely go after modern gaming tropes like the FPS/military shooter with bland colors and make fun of it.