Blue Jays should sign Michael Pineda. Some other intriguing starters who could be realistic possibilities are Michael Wacha, Tanner Roark, Jordan Lyles, Alex Wood, Trevor Cahill and Jerad Eickhoff. Sign two or three of these guys would definitely help solidify the rotation. Pineda, Wood, Lyles or Wacha offer some upside at least. Roark would be a bulk innings guy which would be valuable to this team. Cahill and Eickhoff more brought in to compete for the final rotation spot or as a swing-man/long reliever in the bullpen.
I would say Anderson and Thornton should be locks in the rotation to open up the season, unless they completely implode during ST.
Once Pineda returns from his suspension in May, the rotation could look like this:
Pineda
Anderson
Roark/Lyles/Wood
Thornton
Cahill/Shoemaker/Waguespack or Font as an opener with one of those guys following him.
Kay/Zeuch/Borucki in Buffalo
At least in this case, the Blue Jays have some pitching depth and aren't scrambling to find arms for innings.
I would even target Danny Salazar for a BP spot or as a reclamation project. Doesn't hurt.