Voice123 provides services where you can upload jobs to the website for voice actors to audition for them. It is known to empower voice actors by providing a platform to find jobs and interact with other artists.
Voices.com is one of the largest websites to host many different voice-over samples. You can post jobs and receive auditions, then you will be able to choose the voice that would best fit your animated video.
Fiverr is one of the largest freelance websites where voiceovers can post a job and have it requested by clients. It offers its services for a very low fee. Voice-over artists may also receive a tip from successful projects.
Backstage.com is a paid website that asks for $14.99 per month, but is free to use for new members for a limited time. It has a search engine that allows you to filter only voice-over jobs and specify them by age, gender, and ethnicity.
Upwork works with a bidding system which means you can post a job offer with the guidelines and price you are willing to pay. The voiceover can then offer their price for your animated video.