Here are some suggestions for alternate accommodations:

-          The Delta Toronto (on Lower Simcoe St)
-          The Marriott City Centre (connected to the Rogers Centre)
-          The Sheraton Centre (on Queen St W)
-          Marriott Eaton Centre (connected to the Eaton Centre)

Near the airports:

-          Sheraton Gateway Hotel (Terminal 3 in the airport)
-          Sheraton Toronto Airport (on Dixon Rd w/shuttle to airport)
-          Westin Toronto Airport (on Dixon Rd w/shuttle to airport)

Non-Marriott hotels near the Westin Harbour Castle include:

-          Novotel
-          Fairmont Royal York
-          Le Germain Maple Leaf Square
-          Radisson Admiral