i have iPhone 7 plus without sim card what carrier can I use

As long as its unlocked, you can use any GSM carrier.

If the iPhone is locked to a particular carrier, then you can only use a SIM card from the carrier it is locked to.

Having no sim, does not necessarily mean its unlocked though.

Hi

If your iPhone is locked to a different carrier (such as T-Mobile) than the one that you want to use, then you will need to contact the original carrier (Apple does not perform unlocking) and follow the steps here:

How to unlock your iPhone - Apple Support

Unlocking is subject to the original carrier's policy - a minimum period of paid service and/or a fee may be required.