Nice hotel within 0 to 15 minute walk to pretty well everything.
Toronto has great theatre check out on mirvish.com
Baseball is in full flight, Rogers stadium is a short walk. the Aquarium is right there too.
I would dine down on the waterfront, at the bottom of bay st. (hotel is on bay st.) Not necessarily for the food but for the atmosphere.
Of course you are staying in a large mall and the prices are good with the low dollar right now.
The AGO and the museum are worth a look if you are into that sort of stuff.
If you are a smoker, you can not smoke anywhere and beware the smoking police. If you have a car park it in the hotel garage and leave it there. If you are flying take the UP express unless you have a lot of luggage, it is a five minute walk to the hotel.
Toronto Eaton Centre Marriott is one of my favorite properties. There are lots of shops and restaurants within walking distance. The Pickle Barrel is a good choice and is a short walk from the hotel.
Head down to the waterfront! Harbourfront has some great restaurants and you can take a nice stroll in the area. Head a bit east, and you'll hit the Distillery District. The Gooderham and Worts Distillery was built on that site in 1832, and now it's a swanky area with shops, galleries, and restaurants in heritage buildings. One of my favourites is the Mill Street Brew Pub.
Glad you enjoyed your stay at the Toronto Marriott Eaton Centre! Did you find some good restaurants in the area that you liked?
We ended up eating at an Italian place, right out the back in the courtyard between the hotel and the mall one night, and the Amsterdam Brew House on the waterfront another night. The rest of the time we were attending various nightly parties/events at Microsoft's Worldwide Partner Conference.