You cannot do either successfully. In depth info:
No, it is impossible to breed any Legendary (Latios and Latias are both Legendaries) Pokemon other than Manaphy, who when paired with a Ditto will create a Phione. This is the only way a Legendary can breed. It is also impossible to breed Latios or Latias with a Ditto and get the other one. No Pokemon do this except the Nidoran family, which can create a Nidoran-M or Nidoran-F from the Egg.
Source: Experience with breeding,