How do you pronounce "explanations"?

In American English: /ˌɛkspləˈneɪʃənz/ (ehkspl-uh-NAYSH-uhnz). In British English: /ˌɛksplənˈeɪʃənz/ (ehkspl-uhn-AYSH-uhnz). In Canadian English: /ˌɛkspləˈneɪʃənz/ (ehkspl-uh-NAYSH-uhnz). In Australian English: /ɛksplɐnˈeɪʃənz/ (ehkspl-ⱯN-aysh).

Is "explanations" pronounced differently in American and British English?

Yes. In American English it's pronounced /ˌɛkspləˈneɪʃənz/ (ehkspl-uh-NAYSH-uhnz), while in British English it's /ˌɛksplənˈeɪʃənz/ (ehkspl-uhn-AYSH-uhnz).