Seriously?? Umm, I'll have to respectfully disagree with the above posters. Strasburg is on a strict innings limit, at which time he will be shut down for the rest of the year (I believe that's gonna happen sometime in early September, but you might want to double check on that). Medlen...ehh, take it or leave it.
Cain's numbers coming back down to earth?? That dude's been fairly consistent his entire time in the majors, aside from a few growing pains early in his career. Verlander is quite simply the shiznit. I've been lucky enough to draft him the past two years & dude's been an absolute anchor on my pitching staff. You would see immediate improvement in your ERA & WHIP by adding those two.
If you're confident letting go of Ethier without suffering much of a setback on offense (seems like you could easily replace his numbers by platooning Cuddyer with S. Rod/Patterson based on matchups), then I would go for it. Personally, I would do this deal in a heartbeat.