Your data line does not have to match your WhatsApp number
WhatsApp does not require mobile data to come from the same SIM that was originally used to register the account. Once the account is active, it can use Wi-Fi or mobile data from another SIM.
Do not re-register unnecessarily
Installing a travel eSIM does not mean you should change your WhatsApp number. Keep the existing account unless you intentionally want to move it to a different phone number.
Verification can still matter
If WhatsApp asks you to verify the account again, you may need access to the original number for the verification code. Keeping your home SIM active can make that easier, subject to your carrier roaming rules.
Calls and messages use data
WhatsApp messages and calls use internet data, so they work through the travel eSIM just like they do over Wi-Fi. Video calls use significantly more data than text messaging.
Keep WhatsApp on your existing number, select the travel eSIM for mobile data, and avoid changing the WhatsApp account number unless you actually want to migrate it.