"Maybe it is a bear."
Translation:Det är kanske en björn.
Yes, I've added that. Since kanske historically is made up of kan and ske, 'can happen', several word orders are possible here:
Det är kanske en björn.
Det kanske är en björn.
Kanske det är en björn.
Kanske är det en björn.
The default way of saying it is with det first in the sentence.
But here the reference actually is unknown, because it isn't sure that it's a bear. (Even though I would say "Det är en björn" even without 'kanske'. I think an english equivalent could be "What was that? -It was only my husband." 'Husband' is a human being, so normally you should use 'he'. Using 'he' here would sound about the same as 'den' in the swedish sentence.) These are only my own thoughts and feelings, please correct me if you think I'm wrong. I am not a native either in swedish or in english.
In this case it's det because it's a generic use of the word "it," which is always with a t, not a d. One of the mods earlier discussed this how it's the same with "det regnar" - generically, it's raining. Using den to me would imply "this thing is maybe a bear," referencing something specific. Someone else might have a clearer explanation.