On December 11th, 2012, I received the additional information on BHRR's Cancun and I also knew and was told that he would have been around very few if any Giants for they are not that common Mexico:

Oh yes, as for the Sanson and other dogs… they are not sure how he really is with other dogs because they were unable to socialize him because he was not vaccinated.  I believe he mirrors other dogs.  So if the dog is barking at him, he will bark back.  He spent about 6 months on the streets so they do get accustomed to having the street dog mentality.  BUT, there are many dogs that I have rescued from the streets here, who quickly learn they do not need to defend their territory or themselves.  Once they realize they are safe and the other dogs are not a threat and will not attack them, they really mellow right out and play like the pups they are.  If you need to, I can put you in contact with Andrea and she can explain more.  

Have a great day and thank you again for helping us with Sanson.  We really cant wait to get the photos of him running through the snow!