Vaike makes the most sense. It's weird to picture Owain with not blonde hair, and personality-wise, it's a perfect fit. Plus there's the whole Vaike getting to be Chrom's bro-in-law part, which was Ol' Teach's true motivation all along.
MU. They had built up support and then I thought it'd make the story more "sweet" if MU and Lissa got married since MU and Chrom were best buds. Now MU is a prince and part of the family. MU, Chrom, Lissa, Sumia, Lucina, Cynthia, Owain and Morgan, one big happy family. --- My karma ran over your dogma.