Can I using a 3-phase connection to power 1-phase AC unit?
Both are correct.  The 3-phase breaker is just 3 separate 1-phase breakers with a handle physically connected so shutting off one shuts off all.

Code correctness depends on your local jurisdiction.  In virtually all USA locations, separate uses of each phase allows either breaker setup, while use of all 3 phases on the same device requires the 3-phase common handle breaker.

The 3 separate breakers would be more convenient with 3 separate circuits since you won't turn so much off if one of them goes off.  But there may be a rule that requires this in some location.