Most Significant carrier rule 

For tickets including flights with other airlines than Brussels Airlines the Most Significant Carrier rule applies according to the IATA resolution 302, effective as from April 2011. 

As a general rule, the free baggage allowances apply when Brussels Airlines operates the geographically longest or most significant stretch of the journey. If the longest leg or the most significant stretch of the journey is operated by another airlines, its baggage allowance rules may apply on Brussels Airlines flights or on codeshared flights. The applicable free baggage allowance is mentioned on your electronic ticket. 

Under the consumer protection law by the US Department of Transportation and the Decision issued by the Canadian Transport Authority (CTA) that apply to all flights to, from and across the USA and Canada following baggage conditions apply: 

• Consistency of baggage rules: same free baggage allowance, excess baggage charges and hand baggage regulations are to be applied throughout the journey
• The applicable baggage rules are usually the ones set by the airline listed first on the ticket
• Any airlines listed as first carrier on a ticket can chose freely to transfer the baggage rules to any other airline in the itinerary (MSC).