Canonicalization is when Google tries to combine any URLs together as one when it thinks there might be duplicate URLs. How Google does that can depend on a lot of different signals. John Mueller of Google listed some of the signals Google uses for canonicalization.
John posted on Twitter the following list of signals Google uses for canonicalization:
Here is John’s tweet:
Redirects are a signal for canonicalization, but they’re not the only one. Internal, external links, sitemaps, hreflang, canonicals, cleaner URLs, etc — all play a role. Make everything align, give it time to settle, and leave cookies & almond-milk for Googlebot.
— 🍌 John 🍌 (@JohnMu) July 31, 2020
Forum discussion at Twitter.