Hello aspirant
Cusat and NITs are both nearly equally good for msc integrated physics .Both can be good option .But if I have to chose between them I will go for NITs as they are amongst the most prestigious institutes of india .However it should also be noted that there are several nits which does not have integrated msc physics course so cusat can also be a good choice . NIITs admissions are through iit jam exams and CU sat conducts it's own entrance test
Best of luck