They are described as quite different in the myths. For example, the Titans had much power, whilst the Gigantes drew power from their mother, Gaea. So are they the same or different beings?
The Giants and Gods are different! In the Greek creation myths, Gaea and Ouranos had multiple 'groups' of children. The first were creatures that had "shattering, overwhelming strength" and "a hundred hands and fifty heads". Then came the Cyclopes, and after them the Titans.
Cronus overthrew his father Ouranos. When he overthrew his father, Ouranos' spilled blood created the Giants (and the furies as well!).
The Gods are the product of Cronus and his wife Rhea. Cronus was told that a child of his would overthrow him, so he ate his children. Eventually, Rhea sought help with Gaea and they tricked Cronus with a rock wrapped in blankets. Meanwhile, Zeus was raised somewhere else and later overthrew his father Cronus and freed his five siblings (Hera, Demeter, Poseidon, Hades, and Hestia (not in that order)).
The Titans, Giants, and Gods all had powers and were respected in different ways, but the Titans and Giants were a product of Ouranos, while the Gods were the Product of the Titan Cronus.
So they are different beings.
Mythology by Edith Hamilton
If you mean the giants that tried to storm mount Olympus they are technically half siblings of the titans as they were the result of the union of Gaea and tartaros the primordial god the Greek version of hell was named for but there is 1 notable giant that was a son of Poseidon and Gaea his name was anteus and he was featured in the Hercules/Herakles myth he challenged herakles to a wrestling match because while he was on the earth he couldn't be hurt but Hercules lifted him off the earth and killed him