Well yeah it's not cannon but I could see why. It's implied a fair bit in Awakening (not Ninian x Eliwood levels obviously but still implied)
Anywho, my ships as per the OP's request, let's get started. I normally do my ships based on unique situations in supports or unique pairings that just kidna feel right (even for the Avatar mind you). Also this is in order of when the girls are recruited.
Lissa x Lon'Qu- Owain mentions his dad dying by an arrow. This almost happens in Lissa's Supports with Lon'Qu. So I took that as a good sign. Furthermore, Owain is said to be bad at magic and physical combat in Warriors, and if I'm not mistaken the only person to give him mediocre growths in both is Lon'Qu. If Owain was any better at magic I'd go for Henry though.
Sully x Kellam - Umm, Kjelle. That should about explain it. If somebody doesn't seem the similarities between Kellam and Kjelle, pinch me. Though I'm not sure how popular this pairing is.
Miriel x Gregor/Stahl- This one is a bit harder for me to pick. Laurent mentions that he has nothing inherited from his dad save for hair color (which makes it hard to pinpoint his father). However they mention that his smile is unique, since his father says that he inherited his laugh. Other than that, if he's that generic of a man, it's gotta be Stahl, since Miriel herself says he's strangely generic.
Sumia x Chrom- As stated before. It's implied in the Opening, Lovebirds/The Rescue CGI when Chrom stares blankly at Sumia. Not to mention she talks a fair bit in the game outside of her recruiting chapter and even Maribelle mentions how she's staring lost in the distance when he's not around.
Maribelle x Donnel- First off Brady says Ma the way Donnel says it. If that's not enough proof, then Brady mentions how his father never had tea with his mother, and the only male to not have tea with Maribelle in their supports is Donny (if I am not mistaken, correct me if Im wrong)
Panne x Virion- I know a few people that pair Virion with Cherche and Olivia and those two to me have other, better pairings (stat and story wise). Virion x Panne makes sense to me because his son literally states that he's stalking his father to stop him from cheating on his mother. Virion is the only man insane enough to cheat on a woman that can rip him in two. That and I swear that Yarne got his lack of courage from his father, who subsequently ran from his own people.
Cordelia x Gaius/Frederick- Also a tough pick. Frederick because he admits that she would never stop loving Chrom (something Severa says in her supports with Cordelia). or Gaius because it is apparent that Severa has a seeming weakness for sweets, since she will only talk to Cordi when given a bowl of sweets.
Nowi x Ricken- Now, if Virion wasn't glued to Panne due to Yarne literally saying his father is going to cheat on his mom, then this would be Virion. However, Ricken fits the bill here. The boy blunder mentions how he wants to be a man, and how he keeps looking for ways to be treated as such. Another thing to note, is that Nah says that her father is younger than her when she returns, and how, surprisingly, her father got her mother pregnant before marriage and how they married quickly. This makes me think Ricken saw this as a way to be manly and got her pregnant. Story wise it makes sense to me.
Tharja x Henry- This one took me a bit but I decided after a while that it wasn't Gaius. Gaius himself is immune to curses to him getting cursed in Noire's stead breaks that. Henry however never cares for curses, so this wouldn't matter to him, and Tharja herself falls for him at the S Support when he blatantly says he'd kill for her. This would also explain where Tharja got her idea for the curse on Noire regarding the insane secondary personality. A good baseline would be in her blood, so it'd be easier to draw it out.
Cherche x Vaike- Gerome looks like a regal Vaike (has his same hairstyle). Gerome mentions his parents having died saving kids in some mountains (or some orphanage I forget the specifics), and in their ending they travel the world helping children ( so it fits with me). Furthermore, the father needs to be close to Minerva, like really close. And Vaike literally plays and wrestles with the damned thing. So that's a boon for me.
And Olivia x Robin- This one I based on story (and slowly fell in love with ever since). Inigo's support has his father chastising him for a tactics meeting, as well as comparing him to Lucina. Then it's someone close to Chrom. I found Robin to be a perfect candidate, he sets up the meetings and I'm sure that he'd compare Inigo to Lucina innocently since he's practically glued to Chrom's hips. Robin and Olivia interact in Inigo's recruiting chapter, something unique and not done in the other ones with any other pairing. And Inigo in Fates furthered my suspicions since he says that Robin is the only person to ever see through him, and the only person to really know Inigo's true intentions and feelings is his father who knows why he acts the way he does, not to mention that Inigo got hella emotional when talking to him so the connection just makes sense.
Go ahead and tell me why I'm crazy, I can take it XD