A variant parameter may preselect a particular product option. That does not mean every parameterised address must become a separate canonical product page. Inspect selection behaviour and indexing signals independently.
In a fictional example, /products/mug?variant=123 selects a blue mug. Check both whether blue is actually selected and which preferred URL appears in the delivered HTML.
Inspect the implemented theme
Open a variant link in a fresh browser window. Compare its image, label, price and availability with the product form, then inspect the canonical element. Shopify provides the Liquid canonical_url object for themes, but customised output still needs inspection on the delivered page.
Record discrepancies separately. Losing a variant parameter during a redirect affects product selection. A conflicting canonical affects the preferred content address. These may coexist without having the same remedy.
Decide from the actual product range whether variants need independent content for distinct search intentions. Do not create extra pages solely because a parameter exists. After a theme change, test the main product, a direct variant address and the basket. Preserve the selected option while expressing the intended content structure. Use the indexability checker to inspect the delivered canonical.