IF it's a Marvell title it's likely going to be another Spiderman as there's a new movie being released soon or Thor. I don't foresee Black Widow being a viable candidate. Black Panther ... mmmm probably not? I realize another BP movie is on the horizon but he's not really considered a hot marvel character.
I HOPE it's not Antman. While Scott Lang has a quirky lovable character I cannot imagine the call outs. It'd just be weird.