The thing I don't like about going with the QB competition next year, is there's usually too much team politics that figures into these things. I'd also like to see what kind of competition are you really bringing. Are we talking the likes of Mariotta, Tannehill, McCarron or reaching for a rookie QB in the draft? Or are we talking the likes of Newton or Bridgewater?
You gain nothing by cutting Trubisky and there's the dead cap. I don't believe you can get anything of worth for him in trade but that's an option to just unload him for a late round draft pick.
Assuming the more likely scenario that he'll still be with the Bears is true, I think rather than a QB competition you want to just hold on to him that final year as a backup and bring a QB you have the full intent of making your starter. I'm not a fan of Newton and looking at the fall of Allen since they shut down Cam, that trade doesn't seem as likely as it once did. Would be very intriguing if Bears could bring in Bridgewater though. You wouldn't do that to have him compete. He'd be your starter.