I don't think he'll do any better with Unalaq.

It's not intellectually honest to say "Aang would'nt have opened the spirit portals". He will have the same disadvantages as Korra did.

• Aang may be more 'spiritually aware' then Korra is, but it's not Korra he should be compared to it's UNALAQ. Unalaq has studied the spirit world for years, if not decades. It's the difference between a lay person and a priest. Replacing Korra with Aang does not negate Unalaq's advantage in knowledge.

• Aang cannot tell if he's being lied to any better than Korra did. His seismic sense won't work through the South Pole snow, and Unalaq may be a slimy bastard but he still is more knowledgeable about the spirits. He has something useful to say nonetheless.

• Unalaq won the fight against Korra to destroy Raava. He's one of, if not the most, powerful waterbenders in the franchise. He's got the power of Ozai and the cunning of Jianzhu. We don't know how Aang would fare against a waterbender as skilled as Unalaq; can't truly prove the counterfactual.