Which character in Hamlet (the play) could be a foil to Macbeth (the character)?

Actually, Hamlet, the tragic figure of Hamlet, one of Shakespeare's tragedies, could serve as a foil for Macbeth, the tragic figure of Macbeth, another of Shakespeare's tragedies.
Remember that a foil doesn't have to present the ideal way of handling a situation in contrast to the tragic hero's way of handling a situation. A foil just presents a different way. Laertes, for instance, handles his situation, which is of course similar to Hamlet's, with impetuous and hot-headed anger; he's quick to violent action. Hamlet, in contrast, is contemplative and logical and investigative. Whether he is guilty of a "delay" or not can be argued, but whatever the reason, his vengeance takes the entire course of the play to be enacted and never involves reckless passion like Laertes's does.
To connect the two plays you ask about, remember that Hamlet's revenge against Claudius would result in Hamlet's ascension to the throne if Hamlet were to survive. Ascension to the throne is what Macbeth is all about in the play bearing his name. Both Hamlet and Macbeth are one assassination of a king away from being kings themselves at or near the beginning of their respective dramas. Yet, I say remember when referring to Hamlet, because Hamlet does not dwell on this aspect of the situation. His concern is with knowing the truth about his father's death. His reaction is to "put an antic disposition on" (Act I.v.171)—to pretend to be mad or insane like a court jester—in order to determine the authenticity of the Ghost and the truth of its version of events. You see, Hamlet wants to avenge the assassination of a king.
Macbeth, on the other hand, wants to assassinate a king so he can become one. He is guilty of the heinous act that Hamlet wants to avenge. Hamlet's thoughts are far removed from the fact that killing Claudius would make him king, while Macbeth asks himself:

Why do I yield to that suggestion
Whose horrid image doth unfix my hair,
And make my seated heart knock at my ribs
Against the use of nature? (Act I.iii.137–140)

The unnatural suggestion that creates the image that Macbeth yields to and that makes his hair stand up and his heart pound is the thought of his assassinating King Duncan so he can become king himself.
Both Hamlet and Macbeth encounter opportunities that could lead to their being crowned king. Hamlet thinks only of his father. Macbeth thinks only of himself.