The most likely would be Jon and Lyanna( once she's older of course). That would unite houses in the north etc. And Jon and Dany seems like a bit of a longshotI've been wondering about all the possible marriages.
Jon, Sansa, Dany, Tyrion, Olenna, Lyanna (when she's old enough), Arya (work she's old enough), Pod, Brienne, Tormund, and Littlefinger are all single and ready to mingle.
Best thing would be to put them all in a house like The Real World with cameras in every room and see what happens.