is there a "cannon" ending to the first game?
If you mean in regards to which routes you took as MC? No, but they also ultimately all lead to the same place, and you are able to choose at the beginning of
this game what routes you took in the last one. The core story is the same regardless, the choices really only affect how the MC acts towards different characters, and how they act towards the MC (and each other, presumably). Most of the choices other than the "personality" route choice, and things like how you handle Natalie seemingly have any real effect beyond some flavor text changes.
Like, no matter what choices you make with the MC's mother,
she still (presumably) dies in the end, and never does make the attempt to reconcile with the family like all the choices seem to point towards, and obviously no matter what decisions you make with Darla, she still ends up
going to prison for India's dad's death, whether her, you, or neither of you did it, and there are so many other similar choices that seem lead to the same result in the end.
That being said, if you didn't like the individual endings for certain characters you got at the end of the first game, you can always decide to make some different choices when starting up this one.
The only thing I
personally think is "canon" is that it's supposed to be 15 years that MC was gone (I'm not sure if it's stated within this game, or if it was stated during the therapy sessions during the last game, or when specifically, but I'm sure it's said a few times that he'd been looking for Lilith for 15 years), which means, when setting ages, I went with MC and Lilith's daughter being 15, and the rest of the daughters (and son) being 14 - with the assumption that they were born roughly 9 months after her - and then made my decisions on any other kids in the game based on that. But really even that could probably be ignored if people wanted to, honestly.