If a province can act unilaterally regarding foreign policy, we can declare war on it individually. I'm sure that's in the UN-Hague-Geneva-World Bank-maritime law foreign policy manual somewhere.
Their capital city of Ottawa is in Ontario. Any invasion should also capture the Capital as well.
Shame Ohio can't. Canada has been dumping soft lumber into the US for years. Say the Ohio National Guard goes out there and dumps every load into the lake they can find. That'll raise the price there so it's too expensive to buy.