While Alakazam's MM is useless since its based on confuse ray and Jiraya's MM is super scary and idk if Alakazam can actually handle it. Question is, can and will he use it here and how does it work? Once that is answered the match will be decided.
Well, not entirely anymore.
As of Pokemon: Legends Arceus, Alakazam can learn Hypnosis. Whether or not it's in-character for it to use it, IDK. But if it's smart enough, it'd certainly be able to realize to do so.
Although, non-Mega Alakazam doesn't see the future, it's just very smart, so it might not know about outside factors; If Jiraiya can escape Genjutsus, he might be able to escape Hypnosis, too, & the mechanics of chakra (Although, Kadabra supposedly has immense spiritual power, so it might be aware of such a system, whether or not it can perceive it. But maybe Alakazam mentally simulate it?) & escaping genjutsu/Mind Manipulation.
But resisting/escaping Hypnosis is probably plausible enough, even without outside knowledge, that Alakazam might have a backup plan, even if I don't know what.
Otherwise Alakazam constantly looks into the future and sees the entirety of one's past and future, meaning he sees what the opponent will do, thus landing him the advantage.
Citation for non-Mega Alakazam? IIRC, Future Sight fails if there's already a foreseen attack that hasn't occurred yet.
His 4000IQ beyond supercomputer intellect will make it so he knows what to do very fast.
5000 IQ, but yes. (Although, Shield's entry, the newest comparison only puts it "on par" with a supercomputer.
"Technology is incredible!", indeed, I guess.)
What are Jiraiya's win conditions? AFAIK, for this to not be a Stomp (Hax/Intelligence Stomp, if that's a thing?), Jiraiya would need to have no feasible/plausible/reasonably achievable win conditions.