I feel like such a heathen when I say this, especially with all the other answers (though I didn't read through the entire thread), but...
No. I suppose I could start, but I do not know 100% that I'll get married. I don't know what God's plans are for me in that regard. I want to get married, but I'm not sure that just because I want to means I will. I find it kind of strange, then, to pray for someone that may or may not exist, and if they do exist, I really don't know who I'm praying for. Like, "God, if this person exists, then I pray for his strength, character, etc." I think maybe because I like to pray specifically, for specific people, so I guess I just struggle praying in the way you'd have to to pray for your future spouse.