What do Cassius and Brutus discuss at the end of Act 1, Scene 2 in Julius Caesar? Which "side" will Brutus ultimately choose?

Brutus and Cassius are discussing Caesar’s ambition and what to do about it.

Cassius seeks out Brutus and asks him what he thinks about Caesar.  He knows that Brutus and Caesar are close.  However, he still wants Brutus to join in their conspiracy because his name and reputation will help lend them legitimacy.  Brutus tells him he is indeed concerned about Caesar’s ambition.

Brutus promises to consider Cassius’s arguments, but does not make a promise to join them.  He tells Cassius that he does not want to live under Caesar’s thumb, however.

What you have said
I will consider; what you have to say
I will with patience hear, and find a time
Both meet to hear and answer such high things.
Till then, my noble friend, chew upon this:
Brutus had rather be a villager
Than to repute himself a son of Rome
Under these hard conditions as this time
Is like to lay upon us. (Act 1, Scene 2)

Casca comes and tells them that Caesar was offered a crown three times by Mark Antony.  This seems to reinforce their fear that Caesar is making a play for becoming King of Rome.  Brutus and Cassius do not approve of kings.  Rome hasn’t had a king in a long time.  Caesar is dictator, which is bad enough.  They do not want to risk him getting more power.

After Brutus leaves, Cassius tells us his plan for making Brutus agree to join their conspiracy.  He will trick him into thinking that all of the people of Rome want Brutus as their leader.

If I were Brutus now and he were Cassius,
He should not humour me. I will this night,
In several hands, in at his windows throw,
As if they came from several citizens,
Writings all tending to the great opinion
That Rome holds of his name … (Act 1, Scene 2)

Cassius hopes that Brutus will find all of these letters, supposedly from many Romans, begging him to take care of Caesar.  He thinks that Brutus is on the edge, but this will give him the extra push to agree to join them.  Cassius already has a group going, but he wants Brutus’s clout.

At this point, the reader or audience can make a prediction that Brutus will join the conspiracy.  He has said that he is concerned about Caesar’s power and ambition, and he told Cassius to come see him to talk to him again.  We also know that Cassius has a plan to convince Brutus that the people of Rome are on his side.