If you are a US citizen or resident, inherited cash from a foreign person like your mother is not taxable on your federal return. The IRS doesn't impose an inheritance tax. As far as the requirement for any Canadian tax, you would need to contact their tax authorization or TurboTaxCanada.
As far as states, only a handful of states (Iowa, Kentucky, Maryland, Nebraska, New Jersey, and Pennsylvania) have some kind of inheritance tax. Refer to your state's Department of Revenue to see what the requirements are for filing inheritance tax. Please note that any Interest or other income generated from inherited cash would be taxable.