Not surprisingly, only a minority of posters know what what goes behind successful QB play (chuckle at Saints fans who think they would've won 12 games last season if he hadn't gotten injured).
As far as Trevor visiting the Bears - don't think it's the best fit for him as a pocket QB needs at least 2 of the following to be successful - good O-line/protection, weapons to throw to and/or stud RB (who is also a receiving threat), but it probably gives him a decent chance of getting some playing time this season.
Don't know what the Colts situation is at back-up QB, but Siemian would be a good fit (he's basically a Matt Ryan type QB, but with some mobility).