Before version 4, Superstore included the 3-column layout for the product page as a section setting. For the current version, the layout is its own template distinct from the Default product template.
Connect with Products
Assign the template to all or specific products through the Products admin.
Use the Theme templates portion of the products editor, or use bulk editing to apply the template to multiple products at once.
Customize the 3-Column Template
In the theme editor (Customize), use the page selector to open Products, then 3-columns.
In the left sidebar, open Product pages to customize general settings.