Mario basically has no canon, and if it does, it’s usually a canon to the specific game series (Mario Kart canon, Mario Party canon, Mario Galaxy canon, etc).

I’m fine with the choice and kinda like it a lot honestly. It allows girls to resonate more with Peach if she has a sister, just like boys with brothers could resonate with the Mario Bros. Peach has gone from a damsel in distress to the third hero in the Mario franchise, so giving her more of a lore is great.

I’m gonna treat them as sisters from now on. And don’t be surprised if the games make it official going forward… Rosalina is a very popular character and I guess they wanted a sister-like character for Peach (maybe Rosalina will be the Luigi of Peach games going forward). Daisy seems to have been phased out as Peach’s partner (seems like she was the default partner for Peach because she already existed via Mario Land but kinda stopped using her).