Ottawa is well served from the US via the hubs of Chicago (AA,
UA), Detroit (DL), Washington DC Dulles and
DCA (Air Canada and United), Charllote (US Airways), Philadelphia (US Airways) and Newark (United/Air Canada) and LaGuardia NYC (Air Canada/United) and Boston (Air Canada).
Or you can fly directly into Canada into Toronto or Montreal (Air Canada or WestJet) and connect to Ottawa.
[Edited 2013-07-04 00:11:55]