Me and my friend were playing a causal game and got stuck can you use {cancel} on a blood rush ablility
Not quite. Since blood rush is an ability, a card that counters spells (like {Cancel}) would not work. You could, however, counter it with a spell like {Stifle}.
RESOLVED
Thank you
That's right, activated abilities are not considered spells.
Cancel only targets spells. As mentioned above.