Edit - James_tiberous, while there is reason to question whether Garfield saw combat during Morgan's Raid, other players have provided links to a source that says he did. Therefore, you will get credit for a correct answer. You may thank adisciu9 and CheathamHill.
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That would be William McKinley (23rd Ohio) and Rutherford B Hayes (in command of the 23 but also of the entire First Brigade of the Second Kanawha Division consisting of the 23rd, the 89th Ohio, and two cavalry companies)
I think that McKinley and Hayes are the answer to all questions about the War of the Rebellion that include the words "which two future US Presidents...."
Why I don't have the answer - at wikipedia John Hunt Morgan, click on calico, click on calico prints, click on Samuel Pepys, click on Great Plague of London, forgot what the question is.