There is no difference between the words advisor and adviser according to dictionaries, although North Americans tend to use advisor more. Both terms are accepted spellings for the noun referring to someone who provides some form of advice or counsel and who has some expertise in a particular field.
Most dictionaries and linguists agree that both spellings are correct and that the words are interchangeable. Oxford Dictionary confirms that both spellings are correct and “adviser” is the most used spelling, while “advisor” is common in North America, where some speakers distinguish between the two spellings. Oxford suggests that among North American English speakers, "advisor" tends to have a more official or professional meaning, with "adviser" used as a less formal term.