Mass Effect 3 wasn't well optimised for the PS3 hence the crappy frame rate. It's definitely a GPU intensive and bandwidth heavy game both of which are the PS3's weak points. If you look at the alpha effects they are the same full resolution as on the 360, difference being the 360 has a 256GB/s embedded ram + 21.6GB/s to system RAM while the PS3 only has 22.4GB/s video memory bandwidth. A neat trick to keep the frame rate up on PS3 games with heavy use of alpha is simply to use quarter resolution. Unless someone points it out, you won't notice the difference and it's something Bioware could've done but I guess graphical bling was more important to them than frame rate which imo is the wrong choice at least during game play. All PS3 exclusives either ditch alpha altogether or downgrade to quarter res including Killzone 2 & 3, Resistance trilogy and the two Infamous games. In the Uncharted trilogy ND simply replaced alpha explosions with explosions and fire effects that are not transparent but do feature complex speed and density physics which I imagine is afforded by power of the Cell CPU.
The Wii U has more edram than the 360 and a stronger GPU but slower system RAM (though twice as much) and possibly a weaker CPU (it has to be backwards compatible with the Wii afterall) so taking these factors into account I'm not surprised at the 360>Wii U>PS3 result.
