If you're budgeted, you can take the Toronto public transat (TTC). From any of the terminals, ask for instrustion for the TTC bus stop. Get on the bus that goes to Islington subway station. Once you get to the subway station, get on a downtown/east bound train and get off at Yonge/Bloor station (roughly 12-15 stops). Then go upstairs and take the southbound train to the Queens station (4 stops, I think). Get upstairs and you'll be in Eaton Center, which is right beside the Eaton Centre Marriott. From there it's only a 2-3 minutes walk indoor. Send me a PM if you need more instructions.

This trip will cost you $2.25 Cdn cash or $1.90 Cdn if you buy tickets. Journey time: roughly 40-50 minutes. Depending on traffic on the Gardiner Expressway, cabbing will probably take you about 25-30 minutes.