6 countries have a stake in Trump's meeting with Kim Jong Un - here's what all the big players want in coming North Korea talks

"The stated policy of the United States, no matter which administration, is the complete verifiable and irreversible denuclearization of North Korea," Baker said.

"What does the president want versus what does the core interest of the United States versus what is the ideal for many of the individuals in the administration or State Department — I don't there's a single agreed outcome at the moment," he said, adding "that's what's making it challenging on the US side and why you hear sort of very conflicting views on whether Trump should or shouldn't go and what may or may not come from it."

In the first potential rounds of talks, Baker said, the US would like to see "the North Koreans publicly stating and then following through with ending intermediate and long-range ballistic missile tests, publicly stating and following through with an end to nuclear tests ... in return for additional talks and the potential to ease back on ... restrictions to humanitarian aid and maybe even infrastructure development aid."

China is focused on the "technology transfer, manufacturing transfer, infrastructure development in North Korea to facilitate the economic development of North Korea," Baker said.

"This is something China has been pushing for awhile, that if North Korea can be focused on its economic structure then — yeah, they may still have nuclear weapons here and there, but in general they are not going to be causing a lot chaos right there on the border," he said.

"The Chinese top-tier concern is actually the collapse of North Korea," according to Baker, adding it would cause hundreds of thousands of refugees would flow into China, possibly bringing loose North Korean missiles and nuclear weapons.

To ensure this doesn't happen, China would like the sanctions to be eased to "create the space for some form of engagement" and for economic activity to pick up.

"Russia's big issue on North Korea is really utilizing North Korea as an access route to the South Korean market, and to utilize the Rason area as a warm water Russian port in North Korea," Baker said.

"The Russian view of this is they don't have a huge stake in the outcome unless ... North Korea becomes a key ally of the Unites States," he said.

Baker added that the "Russians really just want to have a little easing on the inter-Korean issue because they have all sorts of plans, for example, to run Russian natural gas by pipeline through North Korea into South Korea."

"The short term issue for [South Korea] is stop this sense that conflict and war is imminent," Baker said.

"They're having a tough time already with the structure of their economy ... it's even worse when the political risk concept is so high," he said, adding "I mean, who really wants to change their investment in South Korea if you're worried that at any moment the US and North Koreans could go to nuclear war."

The biggest thing for Japan is that "there are North Korean medium-range missiles" aimed at them, and that North Korea has been kidnapping Japanese citizens.

"Japan [also] wants to see reduced friction on the Korean Peninsula," Baker said, adding that "they don't really want a strong, unified Korea, which would be economically competitive with them, militarily competitive with them."

In the long term, however, Japan "would like to be able to shift their military attention away from worrying about North Korea, and back to the strategic issue they have with China," he said, adding that that's "why they've been flirting with Russia."

"Japan has a little bit of a tough time here," Baker said. "They've to a great degree been left out of this batch of dialogue."