?page= is necessary for search engines to browse down a discussion. If we set every page with canonical URL to the first post, the search engines will ignore the next page links as duplicates.
If you open a discussion on the first post and check the source, you'll see the canonical meta is the link to the first post.
?page=, every group of 20 posts has its own canonical URL and can be indexed separately by search engines.
Ideally we should use the same