Minato should win high difficulty.
Both have large chakra reserves considering Tobirama is from the Senju clan and Minato is a senjutsu user. Both are extremely intelligent which is showcased by Tobirama dechpiering Juubito's omnyoudan and Minato debunking Obito's kamui.
Tobirama's suitons are teleported away by space time barrier or outright dodged. His gojou Kibakufuda as an offensive weapon against Minato because he can warp away from the explosion. Minato's frog summons get destroyed by gojou Kibakufuda though so I don't see summons being a factor for either side.
This will end up as a battle of speed in which Minato clearly trumps Tobirama, by Tobirama's own admission.