After months of heated debate over his extradition, Luis Guaman will go on trial today in his native Ecuador for the brutal slayings of a young mother and her toddler son last year in Brockton. The highly unusual legal move follows a 14-month battle between Plymouth County prosecutors and Ecuadoran officials over which country should prosecute Guaman for the alleged crimes. US Senator Scott Brown, Plymouth County District Attorney Timothy Cruz and others have demanded as recently as three weeks ago that Ecuador turn Guaman over using the existing extradition treaty between the two nations. Ecuadoran officials has refused, because their constitution forbids extraditing Ecuadoran citizens, and in turn have urged American officials to help them prosecute Guaman.