Thanks for your comments, which help me see how the information on the website is interpreted. It is difficult to be 'exact' regarding Easter shops and services as these things vary according to the establishment, but I can be more a little more precise.
'Shops and supermarkets remain closed' on Easter Sunday and Monday. This refers to the main shops in the towns and all the large supermarket chains. Various small owner-run mini markets and street kiosks (periptera) DO open, but these are at the discretion of the owner so it is impossible to be exact - some open on Easter Sunday, others on Monday, some on neither days and some on both days.
Generally in areas which cater to tourists as well as locals (such as Chania harbour) you will find that nearly everywhere is open over the Easter period - cafes, tavernas, tourist shops, kiosks etc.
Easter Friday is 'a day of mourning' and fasting for the Greek Orthodox church and a number of tavernas in the main towns and villages traditionally remain closed on this day. But some, particularly in areas where there are tourists, remain open.
As Jean says you won't have too many problems, particularly in Chania old harbour.
One other thing - the museums will be closed on Easter Sunday and most likely on Monday too. The site at Knossos closes on Easter Sunday and is usually open on Easter Monday.