A thousand times "no" on Stanton. We just won a WS with depth and diversity and the solution is to change out a bunch of that depth for an oft injured "big name"?
1) Control. Stanton is arb eligible in 2014. He's a FA in 2017. It's hard to say what he wants to do going forward, but he's making millions whether or not he makes it out of spring training this year. Right now he's rumored to have rejected the idea of a long term extension from the Marlins. While this may be partially due to the Marlin's suckitude, Stanton may also want to go the Papelbon route. (Basically, he may or may not have incentive to sign a long term deal with the Sox.) Worst case, you have him for 3 years, during which you'd pay for production via arb. So it's not like he's guaranteed to be a bargain. The only real plus is that he's not a "trade and extend" player like Gonzales was.
2) Durability. Stanton played 123 games in 2012 and 116 games in 2013. He has had hamstring, shoulder, and knee injuries (surgery required to remove stuff from his knee). And he's only 23 years old. These aren't freak injuries (ellsburyesque) - they are injuries which may indicate chronic problems going forward.
http://www.fishstripes.com/2013/4/30/4285344/giancarlo-stanton-injury-hamstring-miami-marlins-analysis
3) Cost of acquisition. While Owens, JBJ and WMB are prospects, they're all under control and they're all somewhat projectable and they all have high ceilings at difficult to fill positions. If one of the three pan out, their value is likely to greatly offset Stanton's, given that they'll cost less and be contributing in a premium position, and while 3b isn't quite SP or CF, WMB's greatest skill is also slugging.
Beyond the prospect cost of acquiring Stanton himself, we'd then need to find a 3b (or SS should we slide X to 3b). We'd also need to find a backup CF - if Victorino gets injured, which he will be, we need someone in CF.
So we'd likely be at: prospects for Stanton, $14 for a SS (drew), prospects for a backup CF, $6 for Stanton's salary?
4) Production. Stanton is a good fielder at this point in his career. When he's in the field. With the bat, Stanton's best skill is power. His career slugging percentage is .525, but last year he "only" slugged .480. While that's good, his 2013 batting numbers are most similar to to Mike Napoli's 2013 (to chose an example close to home). (Napoli was worth 4.1 WAR, but Stanton (due to playing time) was worth only 2.4 WAR.) If Stanton slugs roughly Mike Napoli levels going forward, we'd get good production out of RF, but not superstar/franchise player level. Which people seem to assume is a lock for Stanton.
5) Where to play him? Stanton could probably play in Fenway's RF without trouble. Clearly that's where his value would be the greatest. But if there are injury concerns (hamstrings/knees/shoulder, etc.) you could likely put him at 1B (he played there in the minors). Except we just locked up a 1B. And we have a DH.
The only way this makes sense is for:
Stanton to be guaranteed to be healthy
and play RF in Fenway
and regain his prime power stroke
and want to sign a quasi friendly extension with the Sox
and for Owens/WMB/JBJ to be revealed as flawed players
and for our SS/3B signing to work
and for Victorino to remain very healthy and take over CF without problem (or we trade for a good CF prospect).
