Air Canada is the country's only national air carriers, covering the entire country and international destinations (Note that a number of regional domestic airlines also exist as well as charter airlines serving only international destinations).
As a rule of thumb, all Canadian three-letter IATA airport codes start with a "Y".
Luggage allowance for flights to or from Canada usually operates on a piece-wise in addition to the weight system even for foreign carriers. This means that you are allowed a limited number of bags to check-in where each bag should not exceed certain linear dimensions (computed by adding the length, width and height of the bags). The exact restrictions on weight, linear dimension and number of baggage allowed are determined by the carrier you are flying with and the class of service you are travelling in, usually individual bags may be up to 23 kilos (50 lb) if traveling in economy class.
Additionally, if you are coming from the United States, be advised that Air Canada (on transborder itineraries only - not Canadian domestic service) as well as all US based carriers that operate transborder service (Alaska, American, Delta, United and US Airways) charge checked bag fees. Typically $25 for a single bag of up to 23 kilos/ 50 pounds, and $35-50 for a second bag, unless you qualify for a fee waiver based on elite status or class of service.
