Should I join a CCA in POLY for UNI admissions?

Hi.

Basically I found out from some forums that local govt uni admission = 20% o levels too.

My l1r4 is 18 raw and 17 nett which I know it's not good enough.

Let's says there is 2 scenarios for someone like me:

1) o levels r4:18 , gpa 3.7 to 4.0 (hopefully:), no cca at all

2) o levels r4:18 , gpa average/medicore, cca gold/silver whatever etc

Which scenario will I be MORE 'guaranteed' of getting into a local govt uni?

And also is cca important for scholarships too? Like for overseas universities if my gpa is good enough?

P/s the course I aiming for is architecture/ Life science

since my course is a hybrid course which consists of design and science.

THANKS IN ADVANCE TOO!