We were in Prague for easter five years ago and everywhere was open.
My impression is that czechs don't really celebrate easter at all. Only 33% of czechs belong to a religion and only 11% attend church regularly. The major tradition is roman catholic, but my czech friends are proud of the fact that the czech republic is the most atheist country in europe, apart from estonia.
Having said that I'm sure there will be services going on if you want to attend one. There are certainly plenty of churches!
Prague is a beautiful city, and I'm sure you'll have a great time.
A very early happy birthday to you!