Correia's ERA- over the last 3 years is 129.
158th of all SPs in that timeframe (min 200 IP)
While that 129 does not predict how he will pitch this year, it is descriptive of a performance in the middle of the number 5s. It isn't hard to find data to support that Correia will be a well below average starting pitcher.
I commented because I was surprised to find anything that pointed to something other than a number 5 pitcher.
When the Twins signed him, they must see the 2011 all star and borderline number 3 starter. On those terms, they found a bargain. It is hard to look at the metrics and see what the Twins see.
It is possible that he will put together a few good months, get lucky with the BABIP and perform like a number 3 starter. At that point, the Twins can trade him. It is also possible that he will pitch like Marquis. Most likely he will land somewhere in between, working hard and performing at a level 25-30 percent off league average while taking the ball every 5th day.