Migrate old Bitcoin Core wallet to Trezor
Do I have such a recovery seed?

No. Bitcoin Core does not use mnemonics nor is the seed exportable.

Is there any other way I can migrate my wallet to the trezor? (Other than creating a new wallet and transferring funds from the existing one to this new one)

No. The only way to migrate is to send a transaction that transfers your Bitcoin to your Trezor.

Can a Trezor hold several bitcoin wallets simultaneously? (Suppose I created a new one, and later discovered I can also access the old one through it)

No.