Canal's inventory threshold can be used to change the threshold at which Canal labels your products and variants as “low inventory”. This low inventory buffer can be used to protect or set aside a subset of your inventory and make it unavailable to Storefront partners, thereby preventing overselling.
In Canal settings navigate to the Shipping, Returns & Inventory tab and you'll see the default threshold is set to 25 units. If you choose to change the low inventory buffer, be sure to check the Mark products as "out of stock" to Storefronts at this quantity checkbox. Once your variants reach this quantity, Canal will mark your products out of stock to all Storefront partners.
*For Suppliers using Shopify, you'll want to be sure that the "Continue selling when out of stock" feature is not enabled on your products