Is the North still in open rebellion?

Question

After King Robb died at the Red Wedding and Roose Bolton becomes Warden of the North, there is no one in the North claiming to be a king.

When Sansa marries Roose Bolton's son Ramsay Bolton she comes in contact with some people from the North that say 'the North remembers". Does this mean they are still actively fighting the crown and the Warden of the North? Or are they waiting for someone to take leadership over the rebellion?

Of course, when Jon defeats Ramsay and is named King of the North, they are back into obvious open rebellion.

After the death of King Robb and before the crowning of King Jon is the North in open rebellion against the crown?

Answer 1

Starks ruled the North for thousands of years so the populace finds it really hard to imagine a North without them to lead her.

This is true not just for the peasants but also for the nobles (Re: Lyanna Mormont's letter to Stannis that Bear Island knows no King but King in the North whose name is Stark). Everyone knows what actually happened at the Red Wedding but they were all afraid of Roose Bolton to do anything about it.

The entire strengths of noble Houses were slaughtered at the Red Wedding. When Robb went to war, he took the most likely soldiers with him. The rest were tired after bitter fighting with the Ironborn. There wasn't really anyone left to openly take the field against Boltons and no one to unite them under one flag. Some Lords were bold enough to refuse paying taxes but even they learnt their lesson soon.

Roose: We can't hold the North with terror alone.

Ramsay: You can't hold the North if you let these lesser lords insult us.

Roose: I sent you there to collect taxes, not bodies.

Ramsay: Lord Cerwyn (Thanks to @Kepotx) refused to pay. He said the Warden of the North will always be a Stark, and he'd be damned if he kissed a traitor's boot. You left him no choice. I flayed him living, along with his wife and brother. I made his son watch.

Roose: And?

Ramsay: The new Lord Cerwyn paid his taxes.

Roose Bolton however was not in rebellion. He was appointed the Crown's Warden of the North and he held his office in the name of his Grace, Joffrey and afterwards Tommen of the Houses Baratheon and Lannister.

He trusted Lord Tywin but after his death, he wasn't so sure. He needed the Stark name to legitimize his rule and that of his children. Which is why he made a deal with Petyr Baelish. It was all purely political.

Baelish: Tyrion never consumated the marriage. By the law of the land, she's no man's wife. Inspect her, if you must.

Roose: I leave that to the brothel keeper. It's her name I need, not her virtue.
_{Season 5: Episode 3}

But he still had his reservations:

Roose: When the Lannisters hear I've wed Sansa Stark to Ramsay.

Baelish: The Lannister name doesn't mean what it once did. Tywin is dead. He kept his house in power through sheer will. Without him, Jaime has one hand and no allies, Tommen is a soft boy, not a king to fear.

Roose: The Queen will be enraged.

Baelish: Queen Margaery adores Sansa. Cersei is Queen Mother, a title whose importance wanes with each passing day.

Roose: You noticed, still has friends in important places, whom she can ask for favours.
_{Season 5: Episode 3}

But he did not trust Petyr Baelish. The only reason he was double-crossing Cersei was because he didn't trust her either.

Roose Bolton: "I have something important to tell you. Stop eating and listen. We don't have enough men to hold the North if the other Houses rise up against us, do you understand that?"

Ramsay Bolton: "But our pact with the Lannisters protects us from....."

Roose Bolton: "I had a pact with Tywin Lannister, and Tywin Lannister is dead. The remaining Lannisters are a thousand miles away dealing with that fact. They've never once in the history of the Seven Kingdoms sent their army this far North. If you think they will for us, you're a fool. We've become a Great House by entering into alliances with other houses, and piling those alliances into greater power. The best way to forge a lasting alliance isn't by peeling a man's skin off. The best way is marriage, and now that you're a Bolton by royal decree, it's high time you married a suitable bride, and as it happens, I've found the perfect girl to solidify our hold on the North."
_{Season 5: Episode 3}

And

Roose: A message for you, from Cersei Lannister. A rider arrived from Eyrie, shortly before dawn. Apparently, she thinks you're still in the Vale.

Baelish: A message for me, you say. Strange that the seal is broken.

Roose: I'm sure you understand my position, Lord Baelish. If you received word in the night from the Queen Mother, it does make me question our new alliance. Lannisters made you one of the great lords of Westeros. Yet, here you are in the North, undermining them. Why gamble with your position?

Baelish: Every ambitious move is a gamble. You gambled when you drove a dagger into Robb Stark's heart. It appears that your gamble paid off. You're Warden of the North.

Roose: I had Tywin Lannister backing. Who supports me now? You?

Baelish: The Eyrie is mine. The last time the lords of the Eyrie formed an alliance with the lords of the North, they brought down the greatest dynasty this world has ever known.
_{Season 5: Episode 3}

So In conclusion:

1. the Northmen were not actively resisting the Boltons until Jon came down from the Wall. That doesn't mean however that they were happy with the way things stood. Even then they were afraid as the support from Northern Houses was little to None. Jon had to rely on Wildlings instead.
2. The North was not in an open rebellion against the Crown when Roose Bolton was the Warden. It is however unclear whether Bolton harbored any ambitions for independence given that while he served the Crown, he also married his heir to daughter of an attainted traitor. But of course he had to do it, to provide legitimacy to Ramsay's children and stabilize Bolton rule over North. Aegon the Conqueror did the same thing, Princess Argella Durrandon was "awarded" to Orys Baratheon after her father was killed along with the Durrandon titles and lands. Their Children were seen as heirs of Durrandon Kings and the Baratheon dynasty still flies the sigil of Durrandon Storm Kings and are accepted as their heirs. The Stormlords are fiercely loyal to them.

Answer 2

The North is not in open rebellion with the crown.

Hand of the King, Lord Tywin Lannister, and the new Warden of the North, Lord Roose Bolton, had struck a deal at the Red Wedding, to dispose of the "false" King. And in turn instating the Boltons into (their long sought after) role as Warden of the North.

As Warden of the North the North is no longer in open rebellion. The people of the North may remember the King in the North, and that the Starks are the lawful rulers of the North and Winterfell, but their Leige Lord is evidently in Cahoots with the crown.

It is abundantly clear from the scene above that the Boltons are now in charge, and are so because of Tywin (visible at the start of that inside the episode). The showrunners also confirm that Roose was looking for an escape plan to join the what he thought was the winning side.

Finally, it's worth remembering that most Northern Lords refused the summons of Jon, and decided not to join the Battle of the Bastards, Jon had to rely mostly on the wildlings and in the end the Army of the Vale.

In the below scene we get a bit of insight into the efforts Jon Snow goes through to get the Northern Lords to join him, with the freefolk convinced he struggles to convince even a young Lady of 10 (Lyanna Mormont) to join his cause.

This is futher evidence in a Q&A between HBO and Sophie Turner:

For her to hear that “House Stark is dead” from Robett Glover is a blow – that other houses see House Stark as irrelevant now. But it also makes her all the more determined. It's a frustrating process, because she and Jon are doing damage control and they know it's a lot to ask of these Houses. The odds are against them – Jon is a bastard and Sansa is technically a Bolton.

The Starks are evidently struggling to get support to reclaim their ancestral home, suggesting that most of the Lords themselves we not very interested in the petty war and were happier remaining in their own peace.