With full intel Hiruzen will try his best to end Jiraiya from a distance using Enma and elemental techs with KB and huge shuriken KB so he doesn't enter SM.
Jiraiya will use big toad summoning to stop this from happening but since Enma and Hiruzen canonically drove the Kyuubi out of the leaf village it shouldn't be too much trouble for them to smack the summonings aside especially with the help of his clones.
Jiraiya will obviously have Fukusaku and Shima out by then who can use that tongue thing and high pressure water attack to help J-man's case. Can they alone trim down Hiruzen's KB clones? I doubt it.
A straight up Rasengan is out of the question as Hiruzen is way too equipped to deal with Jiraiya in CQC with Enma.
The three way deadlock happens at around noon so using Hiruzen's shadow (merging with his shadow) to gather nature energy is out of the question.
Hiruzen is just too resilient with these feats to suggest he can't take out Jiraiya before he enters SM. So Hiruzen mid-high diff at most.