Waveshare 1.54 inch ePaper display requires 5Vs from Arduino Uno
The answer lies in the FAQ for that display:


  Why the e-Paper cant work with Arduino?
  
  Answer:
  
  The I/O level of Arduino is 5V, and the e-Paper should be driven with 3V3. If your Arduino cant drive the e-Paper successfully, please try to convert the level to 3.3V
  
  You can also try to connect the Vcc pin to the 5V of Arduino to see whether the e-Paper works, but we recommend you not to use 5V for a long time.


So while you can run it from 5V, you really shouldn't, since you run the risk of breaking it.  

Instead, you should employ proper logic level shifting to reduce the Arduino's outgoing signals to 3.3V and, more importantly, boost the incoming signals from the display to 5V.