Mostly not. They may have opposite personalities. Cancers are home-loving, non-enthusiastic (not sure if that's a real word) and they may get moody most of the time. Geminis are cheerful, attention-loving, youthful, and every bit the opposite of a Cancer. But it actually depends on them.
Scientifically: Astrology has been deemed a pseudo-science because it has failed to pass scientific analysis. No scientific evidence has been discovered to verify any influence the cosmos can have on mundane affairs.
Metaphysically: When understood from an in-depth perspective astrology can be a valuable tool for understanding human personalities, relational dynamics and can be used for advisory purposes to make decisions. It can be quite accurate when done correctly.
It's love, try to win the guy's/girl's heart.