Google Search Index Link [canonical_link] Field for Product Feed

Optional but recommended for better URL consistency

The canonical_link attribute tells Google which URL should be used as the official reference for your product in the Search index.
It functions like the <link rel="canonical"> HTML tag and helps ensure product pages are matched to the right landing page.

When to use

• Optional for all products eligible for free listings.
• Recommended if your link or mobile_link contains tracking parameters or variant selectors.
• Helps avoid duplicate URLs in Google’s index and ensures the correct one is shown in search.

Format

• Type: URL (HTTP or HTTPS, ASCII only, RFC 3986 compliant)
• Limits: 1–2000 characters
• Repeated field: No

File format examples:

Always use the verified domain for your Merchant Center account.

Minimum requirements

• Start URLs with https or http.
• Use the verified domain from your Merchant Center account.
• Ensure URLs are crawlable by Google (robots.txt must allow crawling).
• URL must be RFC 3986 compliant, encode special characters (e.g., & → %26).
• Only submit one canonical_link per product.
• Do not block or redirect the URL in ways that prevent crawling.

Best practices

• Use stable URLs — avoid ones that change over time.
• Remove tracking or session parameters from the canonical link.
• Use clean URLs without pre-selected variants.
• If using URL parameters for the main link, make canonical_link point to the parameter-free version.
• Do not use redirect links (Google may not follow them).

SEO Tip

A clean and stable canonical URL helps consolidate link equity, improves indexing accuracy, and prevents duplicate content issues for variant or tracking URLs.

Official Source : https://support.google.com/merchants/answer/9340054