Please! You only think on Transformers when Shia comes to the table. We are no longer trapped in 2011 or something. Since then he appeared in good movies, such as Fury and, most recently, The Peanut Butter Falcon. He's a talented actor.
As much as I am a fan of Keanu, and as much as I can see him be fit in the MCU, I cannot realistically think in a character for him to portray. I guess that Keanu could play an important vampire in a Blade movie...?