He will certainly be safe at the Montreal SPCA. Yellow Labs with great temperaments are always in demand. They also work with many reputable/responsible rescues.
What did your friend do to try to find his owners? Was he scanned for a chip? I have to caution to be extremely careful when assuming a dog has been abused/mistreated. A dog could be naturally skittish, shy around strangers, or fearful of certain noises/objects because he/she is not used to them. This dog could also have been recently adopted from another family or from a pound/shelter...or he could have been on the run for a while now. His family could be distraught looking for him