The Junior "B" level of the Ontario Lacrosse Association has been around since at least 1964. The OLA Jr B League compete for the J. A. MacDonald Trophy annually at the provincial level. At the national level, the OLA-B has been extremely dominant at the Founders Cup tournament only losing out to other leagues a handful of times in the last 40+ years.
In recent years, the most dominant team recently has been the Six Nations Rebels as they've won the J. A. MacDonald Trophy and Founders Cup five times with four (2007, 2008, 2011, 2012) of the titles coming in the last six years. Clarington Green Gaels had a run between 1998 and 2004 when the Gaels won 4 Founders Cups as Canadian Junior "B" champions and 2 J. A. MacDonald Trophy OLA-B Championships. Of the recent expansion of the league, the Oakville Buzz have been the most remarkable franchise to be built. In 2006, the Buzz team went 19-1 and strolled through the playoffs with little opposition. The Buzz went undefeated at the Founders Cup and crushed the hopes of the host Windsor AKO Fratmen, beating them by a score of 10-4 in the final.
Players from the OLA-B and the OLA-A are often drafted straight into the professional level of lacrosse, the National Lacrosse League.