My daughter was married last weekend in Costa Rica. Her wedding dress was in a normal sized carry on bag that she took on AC to YYZ and then on Skyservice (who allow a wedding dress as an extra in addition to their regular carry on allowance). It was packed by the maker of the dress and arrived in excellent condition - the secret was to have materials that travel well (particularly to a warm climate). On arrival, we hung it up (although finding a place to let it hang freely was a challenge). The other advice was to place it in a steamy bathroom to remove any wrinkles. (And although OT, my trepidation with flying with Skyservice proved unfounded.)