First impression of many, many people when they first stumble upon anime Vanitas no Carte is that main two characters are in love - and while it's not completely wrong and I think it theoretically ultimatelly could be possible (I'll explain it later. Maybe.), after watching or reading this series most of those people feel cheated simply because both Noe and Vanitas technically have love interests of opposite sex. But it's something we could expect - after all, almost no animes outside of BL genre have explicitly non-straight characters, especially main characters. In exchange, in massive amount of series we get weirdly big amount of characters that are only implied to be not straight - by how they are shown, by what they say once in awhile, sometimes even by symbolisms here and there.
But also - existence of one certain love interest in a story not necessairily anihilate possibility of another one existing - either be it simultaneously or later on. And bisexual people exist, so assuming that character is straight only because they showed interest in opposite sex once is just plain stupid. And there is many gay people who were only in straight relationships - sometimes even engaged or married - simply because they didn't realize earlier that they were gay. So like - Jeanne and Dominique aren't an obstacle at all when it comes to thinking about Vanoe not only in headcanons or fanon, but also in terms of what theoretically could become canon. Because, let's remember - this series is still ongoing! Anything could happen and we can only happily theorize!
... Or not so happily, because we all know this series WILL have very tragic ending.
Anyways, the short answer if they are or will became canon or not is: WE HAVE NO FUCKING CLUE.
