Presumably Briskers generally daven nusach Ashkenaz. Is there a particular siddur associated with Brisk, perhaps with haskomos from Brisker roshei yeshivos?
I studied in Brisk. what i percieved from my rosh yeshiva was that they use regular ashkenazi siddurim but incorporate their own nuschaos (ie. most often following the gr"a, for example, ommitting נא in the blessing of rachem in bentching. also ברחמיו in boney yerushalayim. However they don't follow every addition/subtraction of the Gr"a for example they do not add a blessing for modim derabanan or add nachem in bentching on shabbos