By Sam Laskaris Writer The Six Nations Chiefs have earned provincial bragging rights for a third straight year. But make no mistake about it. That is not the three-peat the Chiefs have been coveting all season long. The Six Nations club defeated the visiting Peterborough Lakers 12-7 on Monday at the Iroquois Lacrosse Arena (ILA). With that victory the Chiefs won their best-of-seven Major Series Lacrosse (MSL) final series 4-1. More importantly, however, the Six Nations squad advances to the national Mann Cup series. The Chiefs are the two-time defending national Senior A champs and are keen to capture a third consecutive Canadian crown. They’ll commence their quest for a Mann Cup three-peat on Sept. 5. The Six Nations team will be heading west next week hoping to accomplish its…