Since 2012, several ponies, such as Twilight Sparkle, Pinkie Pie, Rainbow Dash, Applejack, Fluttershy, Rarity, Princess Luna, Princess Celestia and among others have been seen as giants in several giant pony artworks, which is still seen today.
For alicorns and unicorns, they usually can use growth spells (although not all unicorns have this ability). Meanwhile, Pegasi and Earth ponies can use at least growth potions to grow into giants.
I'm thinking that ponies like Aunt Holiday, Hoity Toity, Photo Finish, and some others, should be depicted as giants in artworks that famous MLP artists creating macro art have done from time to time.
Also, some characters, such as Yuma Spurs, Fancypants, and Double Diamond, have received little to no artworks depicting as giants. Examples are shown below featuring some others characters I didn't mention also have received macro art on rare occasions: