When I collaborate I never send a bundle file even if the folks have Sonar. I always get a rough mix made and send them a simple wave or even just email an MP3 which they can load into their DAW and record their parts.
That has always worked well. I think Janet and I swapped bundle files until we realized the MP3 was so much smaller and easier.
The only thing you have to remember is to export the entire track from start to finish. It's OK to trim the end, but NOT the beginning. Be sure the key and tempo are correct, and things are in tune..... then send the MP3. All the other party has to do is import it to their DAW, and record their part.
Once the other party records their parts, they too can send the rough drafts back in MP3 to see if they work ok. Once you decide a track is good to go, THEN you can send it as a WAVE through Drop Box.