Is Doghouse canon to Five Nights at Freddy's?

Yes. Kind of. Any FNAF game released after Ultimate Custom Night will either be retconned or will not be canon to the Doghouse story.

What animatronics will appear in Doghouse?

Two dog animatronics on the main stage, one of them has cool glasses. One cat animatronic and his sidekick in their own garden themed room. One of the humanoid characters that also has cool glasses will be a part of a red themed room filled with prizes. Another humanoid character (this time with a builder hat) will take care of the arcade machines in his construction site themed room.

And for the last main animatronic. She is also humanoid. Hides somewhere in a small warehouse behind the security office. Make sure you keep an eye on her.

Is this fangame based on something other than FNAF?

Yes, of course. 13th of March, 2020. I made a level on LittleBigPlanet based on FNAF with my own characters. Some of them made it into Doghouse. The level (if I remember correctly) was called "Pies Zdzisław's Fast Food, Donuts And Sushi." Yeah, I wasn't really good at coming up with simple names back then. You can also probably guess my nationality by the name alone.

That is all I wanted to tell you right now. I will try to post something soon, but don't expect too much.