Well.. Bioware is surely gonna release some new DLCs for DA2. For DA:O they released about 10 DLCs.
First of all, you need to enable your console. Read on it here:
http://www.gamefaqs.com/pc/988968-dragon-age-ii/cheats.After that, press ~ and type: runscript zz_dae_debug. Then, select the options: World Map Debug -> Initialize World Map -> Act 3.
You should then be able to travel anywhere you want as before you beat the game.
I'm not sure if this may cause any bugs, so have a backup save before you save after doing this.
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To activate secondary quests you may have missed...do these simple steps. These steps do not require you to activate your map (some of them may be, I haven't checked every single quest).
1. Type runscript zz_dae_debug in commands.
2. Click Plot Jump -> Secondary Plots -> One-Offs -> Work with a plot -> Finding Nathalian (you can pick any of them, this is just an example) -> Set Plot flag -> Quest Accepted
There are a bunch of options, and some may and may not work. You have to play around with it.
This may also cause bugs, as with above. There should be a very little number of bugs, if any.
If that's what you meant