Felicidades en su matrimonio! (Congratulations on your marriage!)
because in spanish, there's kind of a big difference between marriage and the wedding celebration itself. And you could always add something sweet, like:
Y que tenga una linda vida llena de bendeciones y mucho amor!
And we hope you have a wonderful life full of blessings and lots of love!
(sounds kinda weird in english but its all good in spanish babyy)