as chance would have it, i was about to post here with some streamlined possibilities that i wrote up based on the earlier discussions. here's what i have:
(1) Cesare is appointed "Cardinal of the New World" by Rodrigo at the same time that he was appointed as a cardinal IOTL (i don't have the exact date written down), possibly because Rodrigo predicts the importance of the Americas and sends him there to secure a foothold (basically like an offshore bank account) if worse comes to worse for the Borgias; at this same time, Juan Borgia becomes a military commander for the Papal States and fulfills his OTL roles, though Juan's death in 1497 may be butterflied since it's rumored that Cesare may have killed him IOTL (though there were others with motive and means to kill him)
(2) Rodrigo dies earlier than IOTL and is succeeded (in time) by della Rovere as Julius II as IOTL, who starts dismantling the Borgia legacy coupled with Cesare's Romagna campaign faltering, so he looks for advancement elsewhere and goes to Valencia, surviving Viana with two options for here:
- either he is captured by Ferdinand and exiled to the New World so that he can't threaten Europe anymore (a Uriah Gambit)
- or he escapes capture and takes on numerous dead-end mercenary jobs (which could have their own interesting effects, depending on the scale of them) so he decides to become a conquistador at about the same time as Cortez IOTL
(3) with a POD at the time of his OTL death, he escapes both capture and death at Viana; this possibility parallels the previous one, just with a later POD and therefore allowing Cesare to keep his OTL roles and reputation, which could have their own effects
(4) Rodrigo never becomes Pope at all, making Cesare a nobody until he gets to the New World and takes on Cortez's OTL role, which not only seems more plausible but also puts him into the criteria of other conquistadors (and from a narrative standpoint it could be interesting; one thing i'm considering as prose is that he and Cortez meet and have a conversation or two on their way to the New World, with Cesare becoming an officially-sanctioned commander while Cortez is eventually imprisoned as a criminal)
(5) the POD is his imprisonment in Aragon, which he doesn't escape from, but is later released by Ferdinand's successor and is commissioned for a New World conquest, giving him legitimacy
also, an interesting narrative which occurred to me is that he travels to the New World on the same ship carrying Gonzalo Guerrero (who also figures into the TL) and falls overboard during the accident that sinks the ship, believed to be dead by Guerrero and the other survivors but he washes up in Spanish-controlled territory, though this one isn't necessarily plausible (but stranger things have happened); after getting to the Spanish Caribbean, he just hangs out for a bit until he signs up/is appointed to the expedition led by Cortez IOTL, possibly usurping command from the official leader (which may even BE Cortez, depending) and it goes from there