If you're looking at air travel, there are three large airports in the area.
- Dulles Intl. Airport (IAD)
- Washington National Airport (DCA)
- Baltimore-Washington Intl. Airport (BWI)
Each airport has advantages & disadvantages. DCA is smaller, closer to downtown Washington, and has Metro rail built into the airport. IAD and BWI are larger, a bit further away, but probably offer more flights.
I don't know where in Canada you live, but don't forget railroad travel. In the USA, all passenger rail is through Amtrak. There are direct or nearly direct trains to Washington, DC from Toronto or Montreal.
www.amtrak.com