While I understand that having this contest on Reddit is kind of the point, the upvote system doesn't seem perfect for this. Is there perhaps a possibility to place limitations on the 'voting rights', for example: You have to be a subscriber of /r/Fantasy for a month before you are allowed to upvote or view on the posts used for this.

Alternatively Google and SurveyMonkey both offer free solutions where the voting could be set up. At this point you could still say that brigading could be an issue, and that is why I would consider making it a multiple choice survey, where you aren't only allowed to select multiple entries to vote on but forced to do so. The number of entries you have to vote for would depend on the overall pool of nominees.