a lot of larger shops have a store locator on their website which will tell you the opening hours for today e.g. here is Tesco http://www.tesco.com/storelocator/
As has already been said , the LAW states that large stores CAN NOT OPEN on Easter Sunday. It is the last remaining part of the old Sunday trading laws.
So no large shops will be open , they are not allowed to by law not by choice.
Small 'corner' shops and 'convenience stores' will be open, supermarket petrol stations will also be open as normal.