Sycraft
It's multi-track. Editor will only load one stereo wave file at a time, studio can load up as many files as you like and work on them together.
Not sure if it makes any difference inside Sonar as a plugin, but that is the difference when used standalone.
I haven't been able to tell any difference between the plug-in versions of Studio and Editor.
I can say, though, that using the stand-alone multi-track feature for cleaning up vocal harmonies is fantastic.
I'm looking forward to more ARA integration between Melodyne and SONAR. The Tempo Map drag and drop feature in 16.03 is a great start.