This is from Foreign Affairs and International Trade Canada site (voyage.gc.ca).
Passports
are ALREADY required for Canadians travelling by air to the US. Get your passports and don't get caught in a time crunch by leaving them to the last.
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Canadians entering and leaving the U.S. by different modes of transportation must carry documentation appropriate to each mode of transportation. See below for details.
Air Travel
As of January 23, 2007, Canadian citizens travelling by air to, through or from the United States must present one of the following documents:
A valid Canadian passport; or
A NEXUS card when used at a NEXUS kiosk
This requirement applies to all Canadian citizens, regardless of age, including children. Canadians should obtain the appropriate required documentation before leaving Canada, keep this documentation up to date and carry it with them when travelling.
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