Good Food in Longeuil?
The St-Charles strip is entertaining, better than your typical suburb, but if you are coming to our fair city as an occasional visitor, I recommend you stay in Montreal, the Metro will bring you back to Longueuil in a quick efficient and safe matter.
St-Charles would be an interesting option for the breakfast before the races, the terrasses offfer breakfast and Ô Gateries is a very good Patisserie for croissant and other french breakfast delights.
There is good food to be found in Longueuil. Not necessarily the most innovative around, but some good solid chow.
On rue St. Charles, right in the middle of "the strip" there's the new Chez Parra. (The old one burnt down a year or so ago.) Very decent traditional French bistro. Clean design, perhaps a bit over-lit, but certainly respectable. (Website: http://www.restaurantchezparra.com/)
A five minute walk away, on rue St. Jean, is Lou Nissart. they serve a lot of classic Nicoise items as well as very decent thin-crust pizzas. (Website: http://www.lounissart.ca/)
Another five minutes up rue St. Jean brings you to Copains Gourmands. I've only been there once, but it was enjoyable. They were quite new then, and still finding their legs. Interesting mix of elegant and casual that doesn't always work (e.g., linen tablecloth but paper napkins -- feels like skimping). The execution of the food was very nicely done, however. (Website: http://www.copainsgourmands.com/)
Otherwise, as other have mentioned, the rest of rue St. Charles is full of standard-fare restaurants. Happily, there are no chain restaurants there. Sadly, the indies that do exist are not particularly inspired. Decent enough burgers and pizzas and paninis and things like that, but nothing exceptional.