If TS did provied a daily schd service (for example) they have the ability to sell several ways:-
Direct bookings with the airline
Sell a block of seats on each flight to 'Bucket Shops/Internet outlets'
Sell a block of seats on each flight to Tour Operators.
In the latter 2 cases,once sold TS get paid,even if the agent cannot sell the seats.
If TS can do this and get it right they are on fairly safe ground in certain markets,providing they can control their costs.
I would advise against a daily service to Portugal though,how on earth would anybody sustain that market?.....CO operate 757's on the route and it's full in summer,not sure about winter,but thats to the 'States'(no offence to Canada).I just cannot see a daily CANADA-PORTUGAL market working,one a week yes,but not daily.