iPad into SONAR...

Been a while since I did it, and I'm using an ipad not a computer at the moment so can't quickly check, but as I remember things -

In Cubasis, go into the "Mixdown" function.

Select Wave as file format and "Create separate files for tracks" unless you want just a stereo bounce of the entire mix.

The files should then show up as available for transfer in the ipad apps window when yiu connect the ipad to itunes and can be saved out from there.

MIDI tracks work in a similar way.

TLW is right on target, I have done this successfully using Cubasis on my iPad, into Sonar. I have only used audio, not MIDI, so I am not sure if that is possible, but at least you get the audio tracks into cubasis. Good luck!

Cubase/Cubasis project files are in their own commercial "private" formats, just like Sonar project files, Logic projects etc.
 
So I doubt Cake could implement an import filter without upsetting Sternberg a bit.
 
Another way to get audio from an iPad into a DAW is to hook the iPad to the DAW via an interface or the iPad headphones socket, play the music on the iPad and just record it in tracks in the DAW. Slow if you've a lot of tracks to work with though.
 
I've worked with Waldorf's Nave iPad app into a DAW, but done it by syncing it's MIDI clock to the DAW via Apple's CoreMIDI, sending it MIDI from iPad apps or the DAW then recording the output as if it were a hardware synth. No idea how you'd do that in Windows though.