After the user confirms that everything is correct on the designed product, you can redirect him/her back to your e-commerce site. On this stage all the product details (e.g. a link to a print-ready file, links to proof images, a URL for opening the product back in the designer, etc.) have been received from Customer's Canvas and can be passed on to your website upon the redirect. After that your website can process the product in accordance with its internal workflow: it can be associated with an order, become available in the customer's account, submitted for fulfillment, or whatever else is needed.
For example, here are the links generated by Customer's Canvas:
The print-ready file can be downloaded from this link
You can return to designing the product by initializing the designer using this link