Do Cardinals Eat Peanuts / Suet?

Yes. Cardinals enjoy large seeds, just look at some of their biology traits: thick and strong bill, curved beak. Peanuts are a right choice, you should definitely include it in cardinals’ diet.

Cardinals also eat suet. It would help if you prepared a suet feeder for the birds in the water, for extra energy needed in the cold weather. Generally avoid serving suet in summer, since it can go rancid in hot weather.

More detail: https://birdingdepot.com/best-bird-seed-for-cardinals/