What do you mean cannon mother?  and isn't Lissa a little young to be perusing? 

Regarding Sumia, the game seems to push her as Chrom's wife: she's the only woman who has limited marriage prospect (four, like Chrom), in the event of a tie in Support Levels she has the highest priority, and she (and poor Cordelia) are the two whose descriptions/conversations with others indicate having a strong crush on Chrom.

As for Lissa...it's a medieval world, and norms were different then? I got nothin'. If it's any consolation, Donnel is supposed to be even younger. Let's not talk about Novi. Please.

Sad part is that I didn't make it with Donnel (I was trying to lvl him up to keep him but he fell in battle since he is so damn weak).  He seemed like too much work too so I let him fall in battle when first introduced to him so he never joined my party after the map.  I like to try to get everyone but sometimes those weaklings are more hassle than good.  I don't really have any sorrow for not getting Donnel considering I could have just replayed map till I got him.

Lissa I thought was in the same 16 to 20 vaguish age that the rest of the mortal characters are in.

Donnel has potential but unless you are using the experience grinding DLC mission, I don't recommend him. Although he does get to be pretty useful once he changes classes.

Unless you're grinding to maximize all of your characters, losing Donnel's actually harmful. His growth levels are unparalled: the first six or seven levels are rough, but by level ten he's caught up to most of your army, and ten levels after that he's a complete beast. Even on lunatic, I feel comfortable letting Donnel handle a dozen enemies by himself for the bulk of the game: on Gerome's Paralogue, I let him solo everything on the far left of the map with nothing more than handaxes and an elixir, with the other units combined having a harder time managing against the center and right-side foes.

Ah, I suppose if I play through on Lunatic (right now I am just doing Hard and Classic) then I'll try to keep him.  Sounds like he levels up pretty good once you get past the start.  It might be a loss but I should be able to easily find another person to fill in his "spot".  I try to level everyone up as much as I can but most FE games I get a basic team down that I know I can count on.

This is why I'm a big believer in EXPonential Growth DLC map. Veeeeery handy, especially in the early going ons for weaker characters like Donnel or Olivia, or when you want Future character to catch up without the hassle of dying (although you do need to be careful with the Lv. 30 Entombed, as they know Counter).

Also, it's pretty obvious that Awakening pushes Sumia for Chrom's wife-to-be (there's even that random cut scene when she rescues Chrom at Regna Ferox). Cordelia's fate when it comes to Chrom is pretty sad though.

However, I have to say that the narrative really comes together in a special way when you have the avatar become Chrom's wife. The dynamic of their friendship and connection is (imo) pushed even further when they're connected by the bond of marriage. Heck, even the connection with Lucina is pushed further because she's now your daughter (It was a pretty powerful moment when Lucina came to the decision to kill you to save Chrom, despite you being her mother as well).

The concept of marriage and having a family isn't really something gaming touches on often, but for Fire Emblem, it was a great move both for gameplay elements and story elements. Kudos.

EDIT: And another reward for having a female avatar. Tharja is totally willing to go lesbian for you. Kinda hawt.

"Ah, how sweet. She's sleeping."
"Sleeping... and helpless."
"Hee hee hee hee."

*Avatar and Thaja's support grew to A*

So it is possible to have a lesbian marriage if your avatar is female?  I suppose no babies from that...  Any other same sex relationships possible?  I was thinking there might be a male on male after being introduced to Libra.

I have Lon'qu and Tharja getting close and soon hopefully marriage right now.

Although there are hints here and there (like the end of game description for Libra...), marriage only applies to heterosexual relationships in the game. Even the avatar has to choose an opposite gender to marry.

Which... makes sense, as the game deals with the concept of having kids that come back and fight for you. And of course FE's world and values are heavily based on medieval European/shogun-era Japanese principals.