Oh, now I really like this idea too; so if I'm reading this right, we could have Marcus Brutus heading the "Ceasarian" faction against the "Pompeians"?
Not going to lie, it's not exactly likely, considering Brutus fought
against Caesar.
However, Brutus was urban praetor under the appointment of Caesar (not entirely sure whether that's for 44 or 45BC) a reasonably significant honour. Mark Anthony by contrast was kind of ignored by Caesar after his debacle in 47BC and, importantly, was only a private citizen in 45BC. Indeed, since Caesar was sole consul that year, Brutus actually holds the most senior rank in Rome at the time.
Frankly, my knowledge is not up to saying exactly what troops were in Rome/Italy at the time. However, considering even with the forces he did bring with them Caesar was still forced to raise new recruits in Hispania, there's probably not a huge number around - otherwise, he'd have taken them in the first place. In any case, if he moved swiftly, I believe Brutus would have reasonable odds to claim their loyalty (if nothing else, he controls the money in Rome).
Plutarch says the following (Dryden's translation):
Caesar, being about to make his expedition into Africa against Cato and Scipio, committed to Brutus the government of Cisalpine Gaul, to the great happiness and advantage of that province. For while people in other provinces were in distress with the violence and avarice of theirgovernors, and suffered as much oppression as if they had been slaves and captives of war, Brutus, by his easy government, actually made them amends for their calamities under former rulers, directing moreover all their gratitude for his good deeds to Caesar himself; insomuch that it was a most welcome and pleasant spectacle to Caesar, when in his return he passed through Italy, to see the cities that were under Brutus's command, and Brutus himself increasing his honour and joining agreeably in his progress.
Now several praetorships being vacant, it was all men's opinion that that of the chiefest dignity, which is called the praetorship of the city, would be conferred either upon Brutus or Cassius; and some say that, there having been some little difference upon former accounts between them, this competition set them much more at variance, though they were connected in their families, Cassius having married Junia, the sister of Brutus. Others say that the contention was raised between them by Caesar's doing, who had privately given each of them such hopes of his favour as led them on, and provoked them at last into this open competition and trial of their interest. Brutus had only the reputation of his honour and virtue to oppose to the many and gallant actions performed by Cassius against the Parthians. But Caesar, having heard each side, and deliberating about the matter among his friends, said, "Cassius has the stronger plea, but we must let Brutus be first praetor." So another praetorship was given to Cassius; the gaining of which could not so much oblige him, as he was incensed for the loss of the other. And in all other things Brutus was partaker of Caesar's power as much as he desired: for he might, if he had pleased, have been the chief of all his friends, and had authority and command beyond them all, but Cassius and the company he met with him drew him off from Caesar. Indeed,he was not yet wholly reconciled to Cassius, since that competition which was between them: but yet he gave ear to Cassius's friends, who were perpetually advising him not to be so blind as to suffer himself to be softened and won over by Caesar, but to shun the kindness and favours of a tyrant, which they intimated that Caesar showed him, not to express any honour to his merit or virtue, but to unbend his strength, and undermine his vigour of purpose.
Neither was Caesar wholly without suspicion of him, nor wanted informers that accused Brutus to him; but he feared, indeed, the high spirit and the great character and the friends that he had, but thought himself secure in his moral disposition. When it was told him that Antony and Dolabella designed some disturbance, "It is not," said he, "the fat and the long-haired men that I fear, but the pale and the lean," meaning Brutus and Cassius. And when some maligned Brutus to him, and advised him to beware of him, taking hold of his flesh with his hand, "What," he said, "do you think that Brutus will not wait out the time of this little body?" as if he thought none so fit to succeed him in his power as Brutus. And indeed it seems to be without doubt that Brutus might have been the first man in the commonwealth, if he had had patience but a little time to be second to Caesar, and would have suffered his power to decline after it was come to its highest pitch, and the fame of his great actions to die away by degrees...
In many ways, Brutus would be an
ideal candidate for a rather dystopian fall of Roman Republic TL. If he moved swiftly and efficiently, he could easily claim to be Caesar's heir (by pointing at Mark Anthony's current disfavour, and maybe even the rumours of his own paternity). On the other hand, he might also be rather acceptable to the Optimates, as he did fight for them. However, the Pompeians are now in a very strong position at Munda, and would likely refuse to reconcile easily. Regardless, you could easily end up with a Brutus being clearly the
primus inter pares - and
not want to be. A Brutus desperately attempting to shore up a failing Republic, whilst Anthony attempts to seize power in Egypt (you
know he would), the Pompeians continuing to hold out in Spain/Africa, a likely rebellious Gaul...
Or, you know, not a horrible ugly death of the Roman Republic. Whatever works.