Q: How do I make sure canonical tags don't sabotage my migration?

Q: How do I make sure canonical tags don't sabotage my migration?

Underrated landmine — wrong canonicals quietly tell Google to ignore your new pages. Worth a dedicated pass.

Short answer: every new page should canonical to itself, on the new domain, over https.

Long answer:
— Crawl the new site and pull the canonical for every URL.
— Flag any canonical still pointing at the OLD domain or http — these came along for the ride and must be rewritten.
— Flag self-referencing canonicals using www vs non-www that disagrees with your chosen version.
— Check that paginated, filtered, and parameter URLs canonical the way you intend.
— Confirm no page is canonicaling to a URL that now 301s elsewhere.

Next step: fix the old-domain and http canonicals first — those are actively undermining indexing of your new pages right now.