Traya's both more powerful and masterful than Maul by a decent margin, in fact I'd say in the Trayus Core she's a whole other tier above him. Her spirit is confirmed to be a stronger dark side entity than Sel-makor and a greater source of dark side power than the Dark Temple on Dromund Kaas.
"I've never sensed anything so alive with the dark side."
- The Empire's Wrath, The Old Republic
As for Surik's own power, Scourge puts her and Revan above all other Jedi:
"For a time I worked with the greatest of your Jedi heroes: Revan and the Jedi Exile."
- Lord Scourge, The Old Republic
"Revan was both Jedi Master and Sith Lord. His student, the Exile, defeated the Sith triumvirate. They were your greatest heroes."
- Lord Scourge, The Old Republic
He has more than enough experience to make the claim:
As the Sith Emperor’s personal executioner, the grimly fatalistic Lord Scourge has personally killed more than a hundred Jedi–and ten times as many Sith.
- Lord Scourge Codex Entry
As the feared "Emperor's Wrath," Scourge enforced his Master's will for more than three centuries. When a Jedi grew too powerful or a Sith too ambitious, Scourge eliminated the threat.
-The Old Republic Encyclopedia
To be fair, the KOTOR II Exile and Meetra are all but different people if one simply looks at their competence. I find it highly likely Drew didn't care to study someone else's character and considering he even sacrificed "his own" character in Revan to the Vitiate wank of that novel, I'd say without reservation that KOTOR II "Meetra" is the more powerful version.
That being said, Maul is a rather inconsistent character and I feel like this comes about from simply being portrayed in multiple forms of media and by different people regardless of who/what the character truly is. IE: It's to be expected.
Operating under the assumption this is Maul as of SoD to give him his best chance, that is all it really is, a chance and to be frank not a very favorable one. If we assume that by "Meetra" this is also the canon LS Exile then by the end of KOTOR II then I don't think the team will slaughter him in sabers given that Meetra would be more inclined to fight defensively and I doubt Scourge's ability to deal a killing blow without more active application of skill from his partner. That being said, the team would eventually win the saber duel as I also find it an impossibility that Maul kills either one of them quickly, he then proceeds to get frustrated as he is oft to do (one of the few things kept truly consistent with the character) and dies via over-extension after a moderately difficult duel if it is kept just to that. It also goes basically without saying that Maul's dueling prowess is > his realized force power and given the power of his two opponents he's not going to be able to use the Force exclusively against one without the other punishing him for it. Basically leaving him in the above described position where as his options and stamina dwindle frustration will set in and Maul will slip up for the loss.
As a little joke here at the end: Likely from tripping over a rock and impaling himself on his own saber or something equally retarded.
@AP:
Her spirit is confirmed to be a stronger dark side entity than Sel-makor and a greater source of dark side power than the Dark Temple on Dromund Kaas.
As for Surik's own power, Scourge puts her and Revan above all other Jedi: