May I marry on a Sunday?
Yes, a couple may get married on a Sunday subject to the availability of the parish and priest. There are only two days on which a wedding cannot be celebrated (Good Friday and Easter Saturday).
Outside of those two days, the sacrament of marriage may be celebrated, but there is a caveat. During the Sundays of Advent, Lent, and Easter, there cannot be a ritual Mass on a Sunday (GIRM, 372). Therefore, on those Sundays, the couple would be married at a Mass in which the prayers and readings are from the Sunday Mass of the day rather than a nuptial Mass. On those Sundays, the Order of Matrimony without Mass may be fully used.
This, of course, is subject to the availability of the parish and priest. Some parishes simply cannot reasonably accommodate a wedding on a Sunday, and some priests have too many things on their schedule to accept a Sunday wedding.