A "foil" is a literary term that describes one character that stands in contrast to another, usually in the same story. However, the characters Winston Smith from 1984 and John Preston from the movie Equilibrium certainly have enough differences and similarities to write about in your assignment.
For starters, both characters are similar in that they live in oppressive regimes. Winston lives under the rule of The Party, which demands absolute loyalty and rewards its citizens for betraying friends and family who may not be loyal anymore. John Preston lives in a society that solves conflict by making its citizens suppress emotions.
This is where the similarities end for the most part, however. But this is good because it means that you can write about how the two characters diverge, revealing much about their character. Winston is in the government, but at a low level, in the Outer Party. John Preston is a “cleric,” which is a respected and high-ranked position.
Winston also moves towards accepting The Party as unbeatable at the end of the novel, whereas John Preston eventually elects to fight against the regime at all costs. One approach you can take in your assignment is showing them on almost opposite paths, since Winston moves more towards rebellion early on, and more towards acceptance of the oppressive regime later.