The Dominion of Greater Canada was formed from the descendants of Canadian Freedom Fighters. While in the Greater Midwest Commonwealth there was acts of lone wolf terrorism or even small communist aligned cells and the occasional riot, just over the border there was a full blown insurgency. Thousands of patriotic Canadians had flocked to join the resistance against the American occupation. Many were veterans of the Canadian armed forces and brought their expertise with them. These groups represented a serious challenge to the authority of the USA as they launched numerous raids and ambushes on American personnel. A focal point for the resistance was southern Ontario. This area was a key transit hub for goods coming from northern Canada heading for the manufacturing centers along the Great Lakes. The Windsor-Detroit crossing was especially important for military goods which came right off the assembly line in Detroit to be sent to the Alaskan frontline.
The scope of the resistance was such that there was a permanent garrison of Power Armoured US army troops in Windsor who aggressively patrolled the countryside during the day but retreated behind their defenses at night. When the bombs fell most of these troops were killed as Windsor took several direct hits. The survivors were overwhelmed as the Canadian resistance, whose forest bases had survived the bombing, drove them across the River. Canada had been liberated, but victory was short lived as the radiation set in. The Canadian Resistance was forced to abandon Windsor and its plans to march on Detroit and reenact the war of 1812 and focus on survival. For several generations their descendants would eek out a living in the southwestern Ontarian wasteland.
80 years after the bombs fell they had reorganized themselves, lead by the last survivor of the League of the Martyr Sir Isaac Brock - a former resistance unit. Slavers had begun to cross the lake. Once again he called upon Canadian sons and daughters to take up arms to defend their homeland. Slowly his group began to absorb other tribals and small survivalist groups that they came across, uniting them with a Canadian ideology and opposing the slavers from the Erie Stretch and Detroit Metro Wasteland. Naming themselves the OnGuards, their power spread. They spent the next generation clearing out Raiders and mutants which flooded in from the Neutron Falls area. The group began to tax communities for its protection, accusing those who refused of being American collaborationists.
In 2227 the Dominion of Greater Canada would be formed when the Article of Refederation was signed by the surviving communities along the Lake Erie coast. By 2250 they controlled up to the outskirts of Windsor and took the city itself in 2252 after a battle with the Motor City Madmen, invaders from the USA. They made contact with a rising nation known as the Kingdom of Sarn, based out of Sarnia. The Sarnians had been formed by tribals migrating from the east who were finally organized around 2245.
War erupted between the two powers in 2265 and quicly became a stalemate. The Sarnians didn't have the strength to take Windsor while the Dominion had to worry about the frontline with the mutants from Neutron Falls. Discontent rose in the nation and it took the promise of revenge on Americans and power to unite the people behind the reigning leader.