Yeah I'm certain Bran will eventually be King but I just can't think of how he does that.
There are three possibilities I can think of
The problem with this is the fact that the North is going to be too preoccupied with the Others to declare war on the Iron Throne.
It's possible they declare war after the battles with the Others but I just don't think they'd have the power to do that.
Also Jon is more likely to be King of the North than Bran is.
Through inheritance
Like you said if Jon becomes King of Westeros and he dies or decides to not be King. Then he could declare Bran heir since he's his oldest male cousin.
This assumes Aegon and Dany are dead or can't take the crown for another reason.
A Great Council is called to choose a King
This is what the show did but I just can't see why people would choose fucking Bran of all people. He's about 8-9 right now and even with a 5 year gap (which isn't happening) he'd only be 13 which is still very young for a king.
So yeah anything could happen.