As Morosi mentions, a deal would be dependent on the Indians deciding to be sellers before the deadline. Given that they've won their first couple games coming out of the break and are two games above .500 for the first time in more than a month, it's hard to imagine the Tribe looking to sell right now.
There are twelve days until the deadline though, and a lot can change in that amount of time.
Why would the Giants want to do this?
They once had a large lead IN... THE... NL WEST... (sorry, inside joke), but have seen that vanish, and are currently in a dogfight with Los Angeles.
They've got Brandon Crawford at shortstop, and he's a better player than Cabrera or Aviles, so I have to assume they're looking for someone to put at second base, which has been a mess for them this season. Brandon Hicks has gotten most of the playing time there, but he's batting just .162 (worst in MLB among players with as many PA as Hicks) and an OPS of .599.
What would SF be offering in return?
Probably not anything special.
Aviles isn't hitting that much better than Hicks (.269, with a .645 OPS), but he's got more experience and more versatility, both of which are things managers tend to like. Still, I can't imagine anything but organizational filler or maybe a guy with a very outside chance at someday becoming a decent reliever being moved for Aviles.
Cabrera (despite the regular complaints from many Tribe fans) represents a bigger upgrade. His .709 OPS that's slightly above league average, and good for a middle infielder. His defense leaves something to be desired, but second base is an easier position, and in theory he'd do better by moving there. Frankly, it doesn't really matter if he would do better there, it only matters if a GM thinks he will.
He might bring back a B-level prospect, someone with a decent chance of being a role player, and/or an outside chance at becoming a valuable one.
Would the Indians be interested?
Cabrera is the most tenured member of the team, but he's also on his way out the door, with top prospect Francisco Lindor playing well in Double-A Akron, and expected at Progressive Field just as soon as his service time is delayed a bit at the start of 2015.
I don't think the Indians can afford to make Cabrera a qualifying offer, because he'd likely take it, and they'd be stuck paying a player they don't need ~$14.5 million, which is basically what it appears they'll already be doing with Nick Swisher. I think they have to let Cabrera walk for nothing if he's still on the team at the end of the year, so the idea of getting something for him instead is appealing.
They are 5.5 games out of first place though, and just 2 games behind Seattle for the second Wild Card right now, meaning they're very much in contention, and I doubt they'll move Cabrera unless they're really surprised by the quality of the return.
Should the Indians be interested?
I think Lindor could provide about as much value as Cabrera over the final two months of the season, because he'd be a defensive upgrade, so I wouldn't mind a trade, but it's rare that a team moves a veteran who's playing reasonably well for a prospect when they team is in contention, in part because unless the veteran is unpopular, it tends to piss off the rest of the locker room so see "one of us" sent out, and so I understand why the front office would resist moving Cabrera.
If the worst should come to pass though, and the final nine games of this tough road trip should go bad, the Indians could find themselves 9 games out of 1st, and 6 games out of a crowded Wild Card field, in which case they should get what they can for Cabrera. I wouldn't call Lindor up in that situation, because of the service time thing, but just let Aviles play there for a couple months, or bring up Jose Ramirez, and be glad to have gotten something for Asdrubal.