Canned tomatoes for fresh
It really depends on how you're using them.

If you want them for a topping along with your lettuce, cheese etc... they must be fresh.

If you're adding them to your ground meat and cooking them, you're probably better off with a drained can of peeled, chopped/diced tomatoes (convenience wise).

Doing both isn't uncommon.

You could also possibly use the canned tomatoes to make the base of some sort of cooked salsa (more similar to a jarred picante sauce than a fresh salsa).