Renting a car abroad is pretty easy.
If you're in the United States.
Before you leave the United States, you need to arrange an international driving permit (IDP), accepted in 150 countries worldwide and required by many to rent a vehicle.
It “translates” your identification information into 10 languages.
In most European countries, and with most rental companies, you can pick up your car in one city and return it at another with no extra charge.
A no-cost one-way rental allows you to use an open-jaw air ticket and avoid the time and cost of doubling back to a single arrival/departure airport.
Most rental car companies in the USA, including Budget, Dollar and Hertz, allow their vehicles to cross the Canadian border, but make sure to inform your provider in advance and read their terms and conditions carefully.