alright this can go either way O_O
alright let's say both have intelligence on each other, and Jiraiya would already know about the FTG and Minato's abilities since he taught him and saw him become Hokage. The toads on the other hand would possible choose either side, but Ma & Pa are with Jiraiya and the boss toads is difficult but Gamaken would also go with Jiraiya. Also Jiraiya has several toad techniques to deal with every attack, even the FTG as he needs the kunai and if jiraiya knows the abilities which he possible did, meaning he would not let minato get close to him easily, but Minato would not let his guard down at all against Jiraiya no matter what, as Jiraiya is incredible intelligent and can quickly analyse a situation just like Minato. The thought is that if Minato comes too close Jiraiya can transport Minato and the FTG into a toad stomach before he touches him, thought minato would get out again. This match is difficult and very long battle, and IF Jiraiya enters Sage Mode, he would beat Minato, as Minato has FTG, against Jiraiya in Sage Mode with Ma & Pa, Ma & Pa would serve as his eyes and also incredible fast.
Seriously guys this can go either way, but i have to go with Jiraiya (mid-high difficulty)