if you book Florida-IAD-xxx using miles on Aeroplan, the baggage rules are set by Aeroplan. I have no experience with Aeroplan's regulations, but baggage allowances are typically more generous when transatlantic flights are involved. But you may have difficulty booking this on one ticket, unless Aeroplan allows you a stopover in Washington. I have never flown on Brussels Airlines, but I did consider using them on an IAD-MUC award flight later this year. Their IAD-BRU flight leaves IAD quite late at night, so it may not be possible to take the last flight from Florida and continue the next day without exceeding the 24 hours.