Great question — answering as the UphillTech team:
If you have access to variant ids and quantities in the cart, you can use a permalinks for this purpose. Example - http://yourstore.com/cart/70881412:1,70881382:1 More details here - https://community.shopify.com/c/Shopify-Design/Cart-Use-permalinks-to-pre-load-the-cart/td-p/613702
Full answer by HymnZzy: https://stackoverflow.stackexchange.com/a/65062866 (CC BY-SA 4.0).
Need it done for your business? UphillTech.