Canada's Constitution doesn't recognize a local level of government. Unlike First Ministers, mayors have no empowered collective body through which they make decisions about cities and communities in Canada.
As a result, mayors lobby - collectively and individually - federal and provincial officials to advance the interests of their communities. Although this is being done very effectively in Canada (through the impressive work of FCM and otherwise), the dynamic still reflects the historic power imbalance between orders of government.
If there is one thing I'd like to see change in Canada, in the interest of strengthening Canada's cities and communities, it would be this: empower mayors, collectively, to make decisions about urban and local policy issues. This includes infrastructure funding programs, legislation that affects municipalities, programs targeted to address particular issues. Personally, I'd start with big cities, and empower the mayors of these cities to make decisions about some of the most pressing urban issues in Canada.
Mayors have unique knowledge about the communities they serve. Canada is big, and diverse. Mayors are well positioned to inform federal and provincial programs and policy decisions, and ensure they can accommodate the unique conditions and needs of all of Canada's cities and/or communities.
Empowering mayors, collectively, would be a big step forward.