This option is the least likely of the five to happen.
This being said, the Astros are under new ownership, and Jim Crane will likely want to create a bit of a splash in the trade and free agency market this season.
There is already a great deal of talk of the movement of Hunter Pence, and with Pence being their biggest bat in the order, the Stros will need a strong hitter to replace him.
Granted, the young Brett Wallace is entrenched at first base at the moment, but I believe that since Fielder is only 27 years old, if Houston has an opportunity to venture an offer for him, than they would either move Wallace to another team in a package deal with Pence, or the more likely scenario of moving him to third base, where he played in college at Arizona State.
The reason why I say this is the least likely team to contend an offer for Fielder of the five I've listed is simply because of the ownership change. Crane is going to have a lot of pressure on him to make a move with Pence, and whatever trade he makes involving the club's star player will be under serious scrutiny.
There is a chance Crane will enter into his new ownership cautiously and conservatively, in which case a run for one of the top three biggest fish in the free agency pool would seem unlikely.
There is also an equal chance, however, that he will want to make his mark as an aggressive owner with hopes to start a rebuild as soon as possible, in which case this scenario is much more likely to happen.