Multiple slave I2C on different power rails
"Shutting off" the unneeded I2C device will probably not work like you expect. The issue is that the i2c data lines will probably have protection diodes to VCC and GND that are not shown in the datasheet.

What will happen in that case is that current will flow into the data ports of the unused device and parasitically power it and/or  lower the pull up voltage on the data lines.

With other protocols there are simple circuits you can use to prevent this, but i2c is bi-directional so most of those solutions will not work.

The most practical solutions are to either use a shutdown function built into the i2c device, or perhaps use of a different protocol. If you must use i2c, some type of bi-directional switch ic, or a SSR style mosfet circuit might solve the problem.

Related questions:

Is there a good practice approach to powering down peripheral devices (SPI, I2C, UART) which use significant power?

Unpowered devices on I2C/SPI bus