Avril Lavigne is from Napanee, if you are interested.
Anyways, back to food...
You should get some Montreal Smoked Meat into you before you go home.
https://www.yelp.ca/search?find_desc=Smoked+Meat&find_loc=Montr%C3%A9al%2C+QC
Not sure what the current state of the bagel wars is, but the last time I paid attention the border traffic seemed to be evenly split between Canadians driving to NYC for bagels and New Yorkers driving to Montreal for bagels.
Try to find a restaurant serving traditional Quebec cuisine - it's been too long since I've been there but at minimum they do interesting things with pork & maple syrup.
Stop in a St-Hubert for chicken... like Swiss Chalet but better... it was a sad day for Ontario when St Hubert closed down here, and a sad day for Quebec when Swiss Chalet's parent bought St Hubert.
Nanaimo bars... Mr. Submarine... maple syrup pie or sugar pie... Coffee Crisp chocolate bars... Kinder Eggs are illegal in the US if you want to live dangerously...
... if you're into cheese the Eastern Townships (south-east of Montreal) are one of the few places where young, raw-milk cheeses are still sold (look for "route des fromages"...
... Unibroue (one of the early successful microbreweries) is about 15 miles out of Montreal and have been making really good Belgian beers for 25+ years... but they don't seem to have tours so never mind...
... and of course pick up a bottle of Screech before you leave, and have some more poutine
Apparently Canada consumes more Kraft Dinner per capita than any other country in the world, but we're not proud of that.
