Canceling fiddlesticks r

It get's cancelled by hard CC and silences, but you can't cancel yourself. It would be nice to be able to self-cancel it though, and I definitely wouldn't call it broken. It's very unforgiving if you fat-finger the R key.

Just to make it clear, do you mean cancel it yourself or do you mean someone else canceling it?

No, you can not cancel the channel on his ult. He would be rather broken and a player would just consistently spam until they have the right timing to ult in. Just give it some practice, try channeling behind walls etc where they don't have vision and take them by surprise. Your ult of course can be stopped with hard CC by the enemy, which is not an ideal situation.