Just to clarify a little.
When I mentioned level shifters. I meant using them on the i2c signals to bridge between the 3v i2c bus on the MCU and the 5v BUS on the LCD i2c backpack.
I use the 5v from the MCU board to the VCC input on the backpack, then use a level shifter on SDA and SCL signals to connect the 3v i2c signals on the MCU to the 5v i2c signals on the backpack.
Using level shifters ensures that both the master and the slave are not attempting to operate outside of voltage level specs on the SDA and SCL signals.
--- bil