This plugin allows you to use the parent product canonical URL for SEO for product variants.
Let's say you have a product "Umbrella" with three variants; small, medium and large.
Then these products each get their own URL, with their own canonicals;
- https://www.example.com/umbrella-small
- https://www.example.com/umbrella-medium
- https://www.example.com/umbrella-large
The parent product is reachable on https://www.example.com/umbrella.
After activating this extension and enabling it under Settings > Plugins > the extensions' Config page, the canonical of the variants will be the parent product's URL.