I pronounce it a bit like "cor-relation", in IPA like /kor.re'lei.ʃən/ but also perhaps like /ko:.re'lei.ʃən/ ("coh-relation"), and almost never like /ko.re'lei.ʃən/ (~="co-relation"), or never like /ko:r.re'lei.ʃən/ (~"core-relation").
Your IPA transcriptions are a bit off (from what the usual convention for English is anyway). I think you mean /kɑ.ɹəˈleɪ.ʃən/ and /kɔɹ.əˈleɪ.ʃən/ for the first and last, but I'm not sure what you mean by "coh-relation" vs. "co-relation". These seem the same to me, /koʊ.ɹɪˈleɪʃən/.
