Cover STORIES are canon
All of them
Even Jinbe's useless one that I frankly didn't even know that existed
https://www.sportskeeda.com/anime/all-one-piece-cover-stories-complete-list-explained
Cover SPREADS also are canon
Cover PAGES ON REQUEST... aren't canon
Quite obviously
Their content is not an idea of Oda, but of the person who asks it
You could ask Oda to draw Buggy beating Roger, and he might draw it, that wouldn't mean that it's canon that Buggy > Roger
Just go and see, he literally drew all sorts of things that people requested