You can do both! A TFSA is simply a tax-sheltered account that can hold various assets, including stocks, GICs, and cash. Many banks offer TFSA high-interest savings accounts, sometimes with even better interest rates than their regular high-interest savings accounts.
Suppose you have available contribution room in your TFSA (which you can check by logging into your My Account portal with the Canada Revenue Agency). In that case, a TFSA is an excellent place to hold cash in a high-interest savings account.