So do you guys think Cassandra and Sera will be the new Avaline/Isabla Miranda/Jack? In this I mean on the surface they seem to hate each other but really over time become good friends?
Personally, I hardly count Miranda and Jack as 'good friends'. They share a common experience of being on Shepard's crew, and no longer hate eachother's guts by the end of the Citadel DLC. Maybe they'll have a drink together in shared company. But I doubt they will keep in touch, or would have anything to do with one another outside of their association with Shepard and his crew.
As to Cassandra and Sera, I doubt that there's going to be that much animosity to begin with. They'll have tension due to differing backgrounds, but I think Cassandra is too mission-focused to have any major disagreements with any other companions. Nobody will LIKE her, she's too much of a hard*ss for her to get lovey-dovey with any of the companions. But they'll all learn to respect her, since she's willing to put disagreements aside for the greater good.
The way I see Cassandra's personality, she is willing to put aside any personal, professional or political disagreements if the individual in question is willing to work with the Inquisition to close the Breach and bring an end to the chaos. Iron Bull's Qunari past? Who cares, he strong and kills demons. Varric's heavy sarcasm and refusal to sacrifice for the greater good? If he fights for the Inquisition, then he is not an enemy.
I don't think Sera's rebelliousness and dislike of nobility will upset Cassandra particularly, as long as Sera keeps sinking her arrows into the eyesockets of every Shade and Arcane horror they come across.
This, above anything else, is why I think I will end up liking Cassandra the most. She has beliefs and politics. But she knows that there are times when those things must be put aside if the world is to be saved. As Inquisitor, you can count on her to be the pragmatic warrior by your side the whole way. The devs have stated that you can kick any of your companions out of the Inquisition, with one exception. They never named that exception, but I don't see it being anyone but Cassandra.