@sportsmom Montréal is beautiful in the summer and very hard to do it within 1 day. Depending on when you are going in the summer there is so much to do/see, Formula 1 racing, Jazz Festival, Just for Laughs, International Film Festival, etc. In no particular order this is what I suggest. Stay in the WEST side of St-Laurent street of Montreal, where it is mostly English. Based on my experience if you go East then you are in French dominant territory and in some cases they are not friendly to English speaking (even if they are tourist).
- Have a smoke meat sandwich with a black cherry cola at Schwartz's Deli
- Eat some Poutine
- Visit Old Montreal (Saint- Paul street)
- Visit Notre-Dame Basilica (Basilique Notre-Dame)
- Go up the Mont-Royal and have a panorama view of half of Montreal
- Get some bagels from St-Viateur Bagel
- Go to the top on the 2nd tallest building in the city "Au Sommet" (meaning: at the top) for views
- Saint Joseph's Oratory of Mount Royal
- Gibeau Orange Julep on Decarie Blvd (go on Wednesday night to see for free a meeting of classic cars)
- Grounds of McGill university
- Dinner cruise around the city
- Casino Montreal
- Biodome
- Botanic Gardens (maybe not with the boys, they might be bored)
- La Ronde (your boys will not want to leave). It is six flags Canadian style.
- Shopping on Saint-Catherine street (WEST side, such as Peel Street which is near McGill University), there isn't much on the east
- Montreal is known for their restaurants, plenty of amazing food ! Try to stay away from big american franchises, go for local eatery.
On your way towards Toronto (on highway 40) stop by Fairview Pointe Claire for more shopping and grabbing a bite before a long car ride.

Hope that helped!