M2E Pro is Magento trusted (TM) extension which helps to upload your Magento inventory to Walmart marketplace in 3 simple steps :
1. group products with similar characteristics together
2. set up conditions for product selling
3. define data synchronization schedule
that's it! M2E Pro takes care of the rest.
also, M2E Pro natively integrates with eBay and Amazon marketplaces making the multichannel selling process easy and smart.