Semanta Santa, or Holy Week and Easter, is one of the biggest Canarian festivals, the Canary Islands being a Catholic Island. This is between 16th and 23rd March, Sunday 16th March being Palm Sunday (Domingo de Ramos) and 23rd March being Easter Sunday (Domingo de Resurrección) and Easter Monday (Luna de Pascua). Easter is usually in April but it falls very early this year.
21st March is a good time to be in Las Palmas, in the Santo Domingo area (near the bus station) and there are various floats and things to see from 6.30pm onwards. Buses back to the resorts in the South run all night. There are other processions and events throughout the Holy Week and every town and village has something, so check what is going on when you get here. There are gatherings in the churches and sermons (in Spanish, of course!)
There are processions in every main street, where the locals carry statues and icons and almost all the Canarians take part in at least some of the festivities of Semana Santa.