Yep, I guess that is LF's plan, which is pretty much the same end goal as in the books. He already controls the Valve in both books and the show, and he plans to marr Sansa with Robert the Heir/Bolton's bastard. In the books the plan was to go and get the North with Valve's knights, knowing that the North will support them as soon as they see Sansa. On the other side, in the show he plans to again get the North with Sansa but with a marriage with Boltons, and then somehow stab Boltons in their back. With North and Valve under his control, he would easily get Riverlands too and would basically be the most powerful man in 7 kingdoms. The next logical step would either be to go and get the Iron Throne, or just rule those lands.Well.. he already (sort of) controls the Vale, so trying to get control of the north would be a logical next step, especially since he has the Stark heir with him - Littlefinger's end game seems to be a puppet on the Throne, the north would give him the men for a rebellion. They already hinted at how stubborn the northeners are when it comes to following Starks and how the Boltons are excessively sadistic/cruel, so maybe the plan is to "re-establish" Sansa in the north and then in some way stab the Bolton's in the back.
Or they will somehow make Littlefinger cooperate with Manderly/Stannis.
Of course, Stannis coming will be a problem for him. Stannis would likely execute him immediately. Sansa is getting smarter, so no guarantee that he will be able to play her for much longer. And of course, the external actors (Danny, Aegon and probably Jon) which would make sure that his plan won't work even if the other things go well.
Still, it is a good plan though and LF has already achieved much considering his heritage.