There are a
lot more marriageable Nords than any other race, which I suppose makes sense with the province being Skyrim and all, but it'd be nice if there was a bit more variety. For instance, there are only two marriageable Breton females that I know of; one of them requires doing a lot of evil and therefore doesn't fit at all for a goody two-shoes character, and the other is a priestess of the hoochie goddess (aka, Church of Dibella).
List for marriage:
Khajiit: 0 female 0 male
Bosmer: 0 female 0 male
Redguard: 1 female 0 male
Altmer: 1 female 0 male
Dunmer: 4 female 4 male
Orc: 2 female 3 male
Argonian: 1 female 2 male
Breton: 1 female 5 male
Imperial: 5 female 4 male
Nord: 13 female 16 male
I have made a Khajiit and a Bosmer, later to find out they had no spouses of their same race to marry. So, I went around to who was available and decided from there. Each ended up marrying Nord men.
I'm pretty sure Senna is a Breton, so you may need to make a tiny adjustment of -1 Imperial female and +1 Breton. There are two wiki sites that I know of, and one lists her as Breton and the other as Imperial; using the console command to change her race to Breton didn't appear to do anything, but there were some minor changes when making her Imperial.