Very doubtful that Juarez, would have been willing or even able to accept, what would be perceived as a devil 's deal, with Seward.
Basically, cause even if out of necessity, he would have thought to accept it, it would have as immediate consequence the loss of any kind of legitimacy and even his own life...
Given that when the news would reach to his supporters, he would have felt after a coup and/or killed shortly after... Without mention that it would be very harming (politically) for the war effort against the French.
Thing was, this actually did happen (except for the immediate handoff of Baja California). Juarez agreed to a deal similar to what I had in this TL in 1861 but it was Congress which refused to accept.