The exchange of leis at your wedding is your "Aloha", or Love, to that person. When a wedding couple exchange leis with each other at their wedding, they are exchanging their love for one another, it is akin to the exchanging of rings.
"FOR THOSE OF US WHO CALL HAWAII OUR HOME, THE FLOWER LEI IS A SYMBOL OF LOVE. ITS IS ALSO A SYMBOL OF THINGS THAT ARE FRAGILE AND TEMPORAL. A FLOWER LEI WILL LAST A DAY OR TWO AND THEN IT IS GONE. OUR LIVES ARE LIKE THE LEI WITHIN THE SPAN OF ETERNITY; THEREFORE, LIVE WITH TENDER CONSIDERATION FOR EACH OTHER, CONTINUE TO LOVE ONE ANOTHER, AND YOUR MARRIAGE WILL LAST. MAY THE LEIS YOU NOW OFFER EACH OTHER BE RECOGNIZED FOR THE LOVE THAT YOU HAVE FOR ONE ANOTHER."
It is also appropriate to exchange the leis with your guests at your wedding ceremony. You (each of you) presenting your family & friends with leis is your "Aloha" to them for coming to your wedding.
Hawaiian people would greet strangers with flower leis as a sign of "Aloha" and welcome and sharing. The Lei is not a tourist thing, it is a very spiritual Hawaiian gesture which shows respect and love, but most of all "Aloha".
I do not suggest that you just put the leis on each other prior to your ceremony, rather, give and receive the leis as a sign of your commitment of love towards each other, and your love for your guests.
Like the rings, when a couple who live here are married, each will purchase (or make) the lei for the other, like you purchase his ring and he purchases yours.
This is part of Rev. Alalani Hill's ceremony and can only be used by her, although it gives more insight to the lei exchange:
I would like to begin with a very special tradition to us in Hawaii, That tradition is the Hawaiian lei exchange. In the ancient language of Hawaii, the Lei has always symbolized an extension of Love, acceptance and welcome. A Lei that is closed is a never-ending circle and is called a Lei Mana which means surrounding Power. The understanding that God surround your life with his power and continuous love. The reminder that the first lei your parents ever wore was your arms around there neck. This is extended into this exchange. The open Lei symbolized the giving of your love and reminds us of how you extend your arms in love. These Leis symbolize the sealing of this moment in this place for all time. When I give these leis to you, I welcome you to each other and to some of the concepts held sacred in these Islands. The Lei exchange joins 'Ohana. Ohana is two individual families coming together to make one stronger family. 'Ohana joins families and cultures and respect for Religious beliefs in Lokahi (Unity), sharing of involvement and responsibility, through support and solidarity. It is love, loyalty, and forgiveness (Ho'opono pono). These gifts are from the 'āina (land). They were gathered and stung together with aloha. They represent from today how you will weave your own lei of aloha with your experiences together. They reflect the temporal and to embrace and live fully in each moment to malama (care for) and nurture each other each day, each month, each year you live, so this union will last a life time. Malama is a word I want you to remember. Because these flowers or this day will not last. Malama (take care) of each other with each breath you take. Express your love now and share with your partner any words from your heart to be sealed in this moment. Welcome your beloved unto your spirit & into your Family by giving a lei and Honi (kiss with nose), to share the Ha the Alo-ha. This is to share the breath of life. If there are any leis to be given to family are friend's bride and groom offer them now and welcome them to the family.