The Founders' Cup is the championship trophy of Canada's Junior "B" lacrosse leagues. The custodial duties of this trophy fall upon the Canadian Lacrosse Association. The national champions are determined through a round robin format with a playdown for the final.
The original Founders Cup was inaugurated in 1972 by the CLA in honour of "the founders of organized lacrosse," especially "The Father of Organized Lacrosse", William George Beers of Montreal, Quebec. Dr. Beers wrote the first rulebook of the sport and was key to the organizing the National Lacrosse Association in 1867, the forerunner of the CLA.
- Alberta - Rocky Mountain Lacrosse League
- British Columbia - Pacific Northwest Junior Lacrosse League, Thompson Okanagan Junior Lacrosse League, West Coast Junior Lacrosse League
- First Nations - First Nations Junior B Lacrosse League
- Manitoba - Rocky Mountain Lacrosse League
- Nova Scotia - East Coast Junior Lacrosse League
- Ontario - OLA Junior B Lacrosse League
- Quebec - Fédération de crosse du Québec, Ontario Junior C Lacrosse League
- Saskatchewan - Prairie Gold Lacrosse League, Rocky Mountain Lacrosse League
Founders' Cup Champions
(*) denotes in 1972, the Founders Cup was awarded to the Junior "C" Champion instead of the Junior "B" Champion.
- "Hail to the Champions: Six Nations Rebels Win Record Fifth Founders Cup Lacrosse Title in All-First Nations Final". Indian Country Today. 20 August 2012.
- "Six Nations Rebels enjoy fourth straight Founders Cup win". Brantford Expositer. 27 August 2014.
- "Jr B Northmen claim Founders Cup". Orangeville Citizen. 25 August 2016.
- "Orangeville Northmen repeat as 2017 Founders Cup champions". Orangeville Banner. 20 August 2017.