i always thought presa canarios were spanish mastiffs. Not sure where the bull mastiff comes into play.
I've seen one or two Presa Canario's in Hungary where they're mainly trained to be security dogs. Whilst they are large in no way can they be compared to an Arabian horse which is around 1.5m tall and weighs about 450 kgs whilst a Presa is between 56-68cms tall and weighs 39-45 kgs .... quite a difference!