Spark Shipping can auto-map your products using Inventory Files: 

When you set up a vendor, and run the inventory update for that vendor, Spark Shipping will detect any SKUs in the vendor's inventory file that match the SKUs in your store, if they match, Spark Shipping will auto-map them for you. 

You need to make sure the Auto-mapping feature is enabled by going to the Vendor page > Update vendor Setting > Advanced Settings > Enabled Automapping