My name is XXXXX XXXXX I am a General Specialist as well as a Notary Public that performs Ceremonies. I would suggest wearing the suit that is a bit larger for comfort. I am sure there will be dancing, pictures, and a lot of activity. With all that activity going on, you want to be sure you not only look good, but feel comfortable during the time of the wedding as well as the celebration after the ceremony.
I have seen men in suits and women in dresses at wedding, (in a little more of confining clothes), and by the end of the night, they were ready to peel out of what they were wearing.
In my opinion, I would wear the bigger suit for comfort, as long as you are satisfied with the way it feels on and looks good to you. I hope this answer has been helpful. Joan