i am not sure of canadas gun laws in regard to barrel length but in genneral some of the informations that he is giving you is bogus
namly that of the the parts inside the lower, full auto parts are diffrent than semi parts and the seletor does not give the weapon the ability to fire full auto it is the sear that allows for full auto operation. add the sear to the m16 parts and then you have a full auto,
if its semi dont pay more that 900 US dollars