Congratulations on your competitive profile. I will only address the UC’s so I have some major specific data for 2021 admits to help gauge your chances. Also this link will show average admitted GPA and the # of students from your HS that have been admitted to each UC campus:
UCLA does not admit by major into the College of Letters and Sciences so I would use their overall L&S admit rate of 13%
UCB does not admit by major into the College of Letters and Sciences so the admit rate for the College was 16%.
UCSD does not have major specific data but the average Capped weighted UC GPA for admitted students was 4.13 and International relations was a top 10 most applied major with around 1464 enrolled Freshman. UCSD admits into the University first and then into the major.
UCSB does not have major specific data, does not admit by major into the College of L&S but overall had an average Fully weighted UC GPA of 4.36 for Freshman admits.
UCI’s admit rate for Political science was 39.1%.
UCD does not have major specific data but had twice as many Political Science admits vs. IR. Based on the historical admission data, UCD has around a 38-44% admit rate for PS and around a 28-38% admit rate for IR.
UCSC’s admit rate for Politics was 61%
UCR’s admit rate for Political Science related majors was 81%
UCM’s admit rate for Political Science was 74%.
Best of luck.