Science research programme or H3 science?

Hi i’m currently a J1 & considering going to oxbridge for my undergraduate studies (hoping to get a scholarship too). I am passionate about science (particularly in the field of engineering) but idk if i stand a chance of getting into oxbridge. From what i’ve read so far, ppl said that taking a H3 subject is a hidden requirement to get into oxbridge, so i hope to work my ass off to offer an H3 subject at the end of J1 (ik it’s gonna be rlly rigorous but yeah). However, i am also interested in joining a science research programme offered by my jc but idk whether i can cope w my studies, especially coz it requires a full-time commitment & i’m afraid that it may also clash with my CCA (I’m a dsa student so my cca cher expects full-time commitment to my cca).

So i was wondering, shd i take an H3 subject or join a science research programme? And does oxbridge rlly look into enrichment programmes that’s related to the major that i’m pursuing?

Fyi i take pcme (all h2s)