I've listened to the tracks over and over again, and they is very small similarity. Cascada wouldn't purposely 'steal' Lady GaGa's song.
You never know, they could have just heard the song once and liked the track and produced ETD without realising that it was from Lady Gaga and without realising that it was going to be a huge track. The Gaga fans are just assuming that Cascada have 'stolen' the track when they clearly haven't.
The song is very much the style of Cascada, but they are a bit of RnB to the track.