My second attempt at predicting the pairs minus the ones I know already. To be real the term "few" in response to last time is kind of shaking my confidence because there will be repeats but I got more reasoning this time.
Lake Guardians and Dawn: Dawn is from Sandgem Town or Twinleaf depending but both are very close to Lake Verity where Mesprit is. My MASSIVE assumption is that all of the Lake Guardians joined up at Lake Verity because Palkia and Dialga went to the other lakes and have been messing with space and time around them. This is so they can be separated because they are both from the Spear Pillar normally. TLDR, Dawn is no longer a yolo guess
Dialga/Palkia and Mars/Jupiter: If my mistake was being confident about which one goes which I will eliminate that confidence. They are both valid enough to go with either the only true deciding factor is what Chainsaw decided to do. This is what happens when you have two women characters on the same team unlike last time with two women on different teams, knowing what the specific pairing is for them is a coin flip.
Giratina and Maylene: I believe that location has trumped typing here because Giratina is in the Turnback Cave (nice name GameFreak) which is very close to Veilstone City where Maylene is.
Heatran and Bertha: Typing reasoning stands, Heatran is located in Stark Mountain, which Bertha also is associated with in the Dimond and Pearl remakes/remasters. This is also the Battle Zone so her being around isn't out of the ordinary.
Manaphy and Fantina: Seems like Fantina is the one getting leftover. I guess Giratinas ghost-type wouldn't be common knowledge to trainers anyway. Idk what your plan is but my assumption would be its similar to Phoebe in that they assume Manaphy is some sort of ghost. Also oops I called her elite 4 last time that's not true she's just so fabulous I mistook her as such. (More reasoning that I know is me overthinking is that she's from Hearthome City, a city Bulbapedia described as "Hearthome City is a child-friendly city; there are many families and young mothers living there" Manaphy, the mythical Pokémon with the unique breeding attribute, going to a city of family and mothers actually kind of works)
Arceus and Cynthia: This one is the same and looking back at the teaser image, Cynthia is at the Spear Pillar clearly and Arceus is literarily above it this pairing just seems right in my mind.
I will like one more attempt if any of these is incorrect before throwing in the towel but I think my logic is sound with these.