I am a Giants fan, and agree I'd rather have Matt Cain over Prince Fielder, but what can't be lost in this is that Gammons says Hardy and another player could be involved. I would love that package for Cain. By getting Fielder, the Giants would likely have to bring Angel Villalona up as a 3rd basemen, and begin on transitioning him back to that position, but he's still a long ways off. Fielder is just the type of power the Giants lineup needs, and Hardy would be a great acquisition to play SS. He has very good power (which I'd imagine would be down a bit playing in AT&T), and is still a slick fielder (though not as slick as he once was from what I've read). The Giants have used a number of early picks on Shortstops over the last few years, but I don't see them producing in the minors, and none of them possess the combination of fielding and hitting Hardy does. If they got Hardy they could also turn around and deal some of the SS they drafted such as Emanuel Burress, Brian Bocock and others. Also, who knows who that OTHER player could be.
I think it's also important to note how well the Giants have brought along pitchers recently. Whether it be developing them, or simply recognizing talent, the Giants seem to be able to bring top pitching along (Lincecum, Cain and Sanchez is certainly coming along). The Giants also have Bumgarner and Alderson destroying low A and A ball talent. If they develop them quickly, they could certainly help offset the loss of Cain in a deal. Noah Lowry is also still around, though I have no expectations for him, he could still be serviceable, and it's unlikely they could get anything for him in a trade.
If the Giants were to trade Cain straight up for Fielder, I wouldn't be pleased, but if they land Hardy and another player, consider me very happy.