Metamask allows you to connect directly to your Ledger or Trezor hardware wallet. Once connected, it will act as an interface to your hardware wallet. Think of it as an alternative app for your hardware wallet that is more powerful and advanced than the Ledger and Trezor apps. You get the best of both worlds: The security of a hardware wallet and the advanced feature set of MetaMask.
Some sites may have integration with MetaMask but not with Trezor or Ledger wallets yet. Outside of that as well, the software that comes with Ledger and Trezor is very rudimentary compared to MetaMask. In other words, MetaMask gives you much more control and also allows you to add custom tokens to your wallet that may not yet be supported by the hardware wallet software.
Connecting MetaMask to your hardware wallet allows you to do things like:
Check your account balance (ETH, ERC-20 tokens, StakeWise tokens, etc.)
Sign transactions (Send ETH and ERC20 tokens and collectibles, deploy contracts, etc.)
Connect to web3 dApps that don't support Ledger or Trezor directly
Add custom tokens not yet supported by Ledger/Trezor (like StakeWise tokens)
Speed up stuck ETH transactions
Before you begin, make sure that:
the most up-to-date firmware on your ledger or trezor device
up-to-date Ethereum App on the Ledger (from Ledger Live > Manager)
"contract data" enabled on the device (if needed for what you are doing)
ledger live app closed
the device plugged in via USB NOT bluetooth
the device unlocked and in the ethereum app
Ledgers connecting with MetaMask can be broken due to cache, follow this article to fix it
Windows 10 security popup? Try this fix
Once you successfully connect your account, it will behave just like other MetaMask accounts, with the difference that you need to have your wallet plugged in for signing transactions or messages.
If later you want to remove the connected account, simply click the X next to it on the account list menu (MetaMask will remember your account name and tx history if you reimport that account in the future).
If you previously used an account and would like to connect it to MetaMask, make sure you view multiple pages of accounts on BOTH derivation paths (Ledger Live and Legacy).
When you connect your Trezor wallet and the list of addresses/accounts displays, these are addresses/accounts associated with only your Trezor, not your MetaMask wallet.
To use the benefits and features of a hardware wallet, you will need to use one of your Trezor addresses/accounts, not your MetaMask address/account.