personally, I find Canaria's behavior much less stupid and dense than it may seem.
Okay, she doesn't realize how Caesar feels about her, but even if she does, she AGREES not to realize it.
Because his is a purely political marriage, and in politics, the less feelings enter into it, the better.
Moreover, at her age she perfectly realizes that love, especially youth love, soon turns on and soon goes out; only that her husband is the future emperor, and if relationships deteriorate it is quite unlikely that we are satisfied with an "okay, we loved each other, we no longer love each other, friends like before".
Since she has no one to protect her if things go wrong, it is more understandable than ever how she wants to keep herself away from the love and blindness to which it leads as much as possible, so as not to risk being burned.
Ok, it's a romantic manga and so we always tend to think that "Omnia vincit amor", but as an adult who tries to survive in a den of snakes . . . his behavior is the most logical and effective