What role do you think people would play (in terms of results, endorsements, polls, etc)?
My take (not a prediction of what I think will happen)
Trump: maybe Mark Zuckerberg or Tulsi Gabbard
Cruz: Warren
Rubio: Kamala Harris
Kasich: Kirsten Gillibrand
Carson: Jason Kander
Jeb! Bullock
Christie: Cuomo
Zuckerberg is not a good fill-in for Trump, more like some celebrity spewing left-wing rhetoric (or Gabbard)
Cruz is obviously Warren, originally well-liked by the base, somewhat burned by Warren's endorsement of Hillary or in the case of Cruz his originally proposed 'non-citizen legal status bill'/TPP op-ed with Ryan.
Walker is the closer parallel to Harris, both theoretical establishment + progressive unifying picks
Jeb/Rubio is basically an interchangeable category, and Booker fills that role.
The Carson-like candidate might be a celebrity with more minor appeal relative to the Trump equivalent candidate, perhaps more moderate and toned down.
Don't really think there is room in the Democratic field for a Huntsman/Kasich type candidate. Those 2 were mainly propped up in the GOP primary by liberal/moderate independents.