Are there more holes on the north side of saguaro cactuses?

Yes, there indeed may be more holes on the north side of a saguaro cactus (Carnegiea gigantea or Cereus giganteus).

Specifically, the south side of a cactus gets the most sun. Water loss therefore is bound to occur every time that a breathing pore, or stoma, opens up. As a result, the cactus tends to carry important regulatory activities through a greater number of pores out on its northerly side to protect internal water reserves.

Yes too, there may be more holes in terms of those caused by predators. The Gila woodpecker (Melanerpes uropygialis) and the red tailed hawk (Buteo jamaicensis) particularly favor the saguaro cactus as a nesting site. They like saguaro nesting cavities as much as other wildlife enjoy the nesting holes in a deciduous tree. They nibble their way through the saguaro's thickened outer covering to access the fleshy, juicy, succulent tissue on the inside of the stem. On the north side, they satisfy their needs for room and board without having to worry about water loss drying out their food source.