Johnson's doing a pretty nice Pomeranz impression right now, complete with one of the best curveballs in the league and extremely low hard contact (on par with Sale and EdRod). Open question whether that translates back to the rotation, but we have five years to find out. Do you think he's playing that far over his head?
I like Canha's fit here but I'd worry about giving up a cost-controlled starter, even if he settles as a long-term #4, for a guy who's never been able to handle RHP.
Canha has a better career split vs RHP than he does LHP and he's under control until the end of 2021 while Johnson 2023. It is 2 years of control, not 3. Maybe I'm wrong? I think it's a fair question to ask though because there are valid reasons to be high/low on both Canha and Johnson.
Edit: Johnson's last 11 games (since the last time he gave up a HR): 17ip, 18h, 4r, 4er, 14k/3bb and an era of 2.12. Hitters are slashing .269/.300/.299 on a .340 BAbip.
First 11 games: 19ip, 24h, 14r, 14er, 7bb/19k and 4 HR allowed. Hitters slashed .304/.360/.532 on a .357 BAbip.
He's hittable but if he keeps the walks under control and limits extra base hits, he could still be serviceable. Hell, his FIP is 3.55 and his xFIP is 3.97 this season. His GB% is also closer to his pre 2016 performance, where he was much more successful. He's at 41% this year, after being around 35% the last 2. In 2014/15, he was 45-46%.