It turns out that Dwayne "The Rock" Johnson, was offered the lead role in Transformers 4 before Mark Wahlberg. This was confirmed via a tweet during a online Q&A.

Michael Bay offered me Transformers, but I was unavailable due to Hercules. Then Wahlberg was offered the role. #RockTalk @nadydi
— Dwayne Johnson (@TheRock) April 26, 2013

It seems that Bay really like working with both actors on Pain & Gain to offer one, then the other a role. Makes you wonder if The Rock had set yes, would Bay have figured out a different role for Wahlberg. Thanks to Wynton R. for the link.