This game is amazing can't wait for Dlc/sequels, however I read on several different sites that the game is "open ended" yet for me the game has it's ending then when you choose "continue" it just replays the ending.

I'm fine if it's not as I plan on re-playing it several times but I'm just confused as to how so many sites may be wrong.

Now comes the obvious question. Which ending is canon? If there are DLCs or sequels which ending will they canonize in the lore?

There probably isn't a canon ending. Another game in series would probably be a prequel or it would take place in another location that isn't affected by the events.

That is not what that word means. Being able to play after the ending has nothing to do with open-endedness. Open-ended means that you can choose how you approach the game and the situations it puts you into...open-ended means that no single way to play the game can be described as the right way to play it.

They already said it will most likely take place in another location but I doubt they will completely mention the events that are occurring in Dunwall. If it is a prequel, then yes, there won't be a need to canonize any of the endings.