Quo animo - with what intention

Animo cancellandi - with intention to cancel

Animus - Mind; soul; intention; disposition; design; will; that which informs the body.

So the difference is animo is WITH intention and animus is the intention itself, what's governing the intention.

Animus cancellandi - the intention of destroying or canceling. (applied to wills)

with intention vs. the intention itself.

Also, a pronunciation note:

c is pronounced 'ch' when it is before an e or an i.

cancellandi would be pronounced 'kanchellandeye'