Unless something very strange happens they are not bringing in a TOR arm and most likely not a rental, with the possible exception of Dan Haren. Even if it's not Haren the Marlins are a likely trade partner with both Tom Koehler and Brad Hand being talked about. Andrew Cashner is another possibility if San Diego sells him low. Beyond that I wouldn't get your hopes up.
They need to add something for this year's run. Next year they really don't have anything ready. Edwards is still not starting games so I expect him babied for the next 2 years in the pen. Johnson is a year out. Rest are not even in AA yet so don't expect anything emerging for at least 3 years.
So they could try to get a guy for this year and with control over next year. It doesn't cause any issues. Niese would be okay but I wouldn't give up anything of value for him. Mets need O. So I would give them Olt. Wright has been injured too much and Olt would be a solid gain for them. That pushes Murphy back to 2B. Flores to SS.
As an add...I would guess a arm. Mets' O is lacking but I don't see anything the Cubs willing to give up as a improvement to what they have.
2015 28 New York Mets $7,000,000 5.107
2016 29 New York Mets $9,000,000
2017 30 New York Mets *$10,000,000 $10M Team Option, $500k Buyout
2018 31 New York Mets *$11,000,000 $11M Team Option, $500k Buyout
Earliest Free Agent: 2017
So Cubs would be getting the Mets off the hook on his contract. He firs the 2nd LH arm in the rotation. Over all it would be an improvement to Wood/Wada.
Maybe Wood to offset the cash. So Wood/Olt. Then they can not offer Wood Arb and get out of that deal. Cubs get a #4 SP under control til 2017/18.
It wouldn't be that bad. Cubs don't have much in LHSP nearing to the bigs anyways.