Shields for Cano or Haren for Howard?

Currently my pitchers are Verlander, Peavey, Haren, James Shields, John Danks, and Ben Sheets. I have an offer where I would trade James Shields for Robbie Cano. Another offer I have is Dan Haren for Ryan Howard. Haren is better than Shields but Howard is better than Cano, but Cano usually heats up in the second half. What should i do?