There's more than two pronunciations, depending on who's talking, how fast they're talking, and how excited they are.
It's normal to reduce a vowel to shwa /ə/ when it's unstressed, and even when it has only a secondary stress, like the last syllable of candidate. The faster and more excited the speaker, the more likely they are to reduce the vowel.
And to do other things. The first /d/ is frequently deleted: /'kænədet/, and the second /d/ is often reduced to a flap: /kændəɾet/. All of these are independent processes, and may happen together or separately, so all combinations occur.
The technical term for this is Fast Speech Rules, btw. It's a big topic in phonology.