Although both pages are very similar sans the logo color and some verbiage, if we do the rel canonical from GoCentrix->CallRingTalk.com then CallRingTalk.com will be the preferred site for indexing?
** Yes.
You can also add rel canonical to it self on CallRingTalk.com.
Lastly, will having had the duplicate content for some time now have any sort of lasting effect on our potential ranking once we implement the canonicalization?
** No, you are more then safe. This rel canonical will only help google understand what is your preferred version and it will display it accordantly.
Overall the only downside of duplicate content is that Google might show in serps the version that is teh secondary as importance in your opinion - but there is no algorithmic or manual filter / penalty for this even if you don't implement rel canonical.
Hope it helps.
