We’re driving to Montreal on Tuesday, just for a few hours. Suggestions? We were there in 2017; one day was spent initially in the old town section then wandering with @EmilyG ; the next was at the botanical garden. It’ll be both my adult kids, and my friend.
I had an afternoon free in Montreal during a business trip once. A colleague and I decided to walk to the top of Mount Royal, which has a beautiful view of the city. After our descent, we went for a late lunch at Ben’s, one of Montreal’s famous delicatessens.
Ben’s is gone now, sadly, but after your walk up Mount Royal, you can still head to Schwartz’s Deli for a terrific Montreal Smoked Meat sandwich on rye. If you’ve never had Montreal Smoked Meat, you should try it. It’s like pastrami, but oh-so-much better.
Whatever you do, have a great trip!
Bagels, lavash, Montreal smoked meat. And just walk around downtown.
On the “backside” of Mont Royal*, we had a lovely little meal (coffee and croques messieurs) at the Croissanterie Le Fígaro, in a nice, typical residential neighborhood.
*A mentioned above, I also recommend you walk around the park on top and enjoy the view.
Ando, if you’re in the old city, look over the river to L’Habitat, the 1967 take on the future of modular urban housing.
We had a great time touring the Olympic Park a few years ago. It will take at least 2 hours though.
We parked at Quai de l’Horologe and had lunch at a brewpub in the nearby Bonsecours Market. We rode the La Grande Roue de Montréal ferris wheel. Then we drove to the Biodôme and went through that, followed by a Planetarium show. The only downsides were not enough time to come close to doing justice to this lovely city, and being stuck in rush hour traffic on the way out. Google maps could not keep up, leading to time consuming delays. But we stopped at a Tim Hortons outside of the city which improved things! TimBits are better that Dunkin’ Donuts Munchkins!
Sorry I didn’t see this thread until now. I’ve been in the process of setting up my new computer. Glad you had a good time. 
Would love to meet up with you if you’re in Montreal again sometime.
We’d love to get together again, as well!
If it’s a long drive, perhaps consider staying a day or two?
My suggestions would be dated. There are many highly regarded restaurants, some which are inexpensive, especially given the strong American dollar. But picking one, Schwartz’s smoked meat is worth it if you like pastrami and fries, and you get the “medium” one mixing lean and fat brisket. St. Viateur Bagels are excellent. Toqué and Joe Beef are great restaurants, but so is Frites Alors! and many others (mediocre restaurants don’t tend to stick around, excepting a few chains). Any bakery will have good croissants. Any hole in the wall a decent steamie hot dog or steak frites. Are Centropole and Beauty Lunchonette still around?
If the weather is nice, strolling in Old Montreal or in Mont Royal is pleasant. If the weather is less nice, the Montreal Museum of Fine Art may or may not interest you. Maybe the decent bars and jazz and blues clubs are still there close to Crescent Street - dunno.
A quick Google implies Centropole no longer has buxom waitresses serving milkshakes. But Lunchonette Beauty and Frites Alors! still seem to be a thing. I was sad Ben’s closed; we were there many Sundays at noon to recover from the previous night’s exertions. Their fries were better than Schwartz’s and their smoked meat comparable. Much fancier desserts. 
Schwartz’s will usually have a line-up outside, and its smoked meat is over-rated. Check out the alternatives such as Dunn’s (downtown), Lester’s (on Bernard), or if you are approaching Montreal from the west, try Smoke Meat Pete’s on Ile Perrot. $25 or so - sandwich, fries, and drink.
Mount Royal will still have evidence of winter - be prepared for wet grass, and muddy trails in the woods. No problem if you stick to the main paths.
Drive through Westmount and to its Lookout on Summit Circle. Walk in the adjacent woods if not too muddy.
Walk around the McGill University campus. There are usually guided tours offered.
If you’re parking downtown - street parking is difficult. Many office buildings offer reasonably-priced parking.
If it’s pouring rain - take in a museum, or explore the so-called “Underground City” - a long network of underground passages joining shopping centres, office buildings, and transit centres. Or buy a single-ride “A” zone transit ticket ($3.75) and ride the Metro, and/or the new REM from Central Station to Ile des Soeurs (one stop - 10-15 minutes each way) and back (going further will cost you more). Stand at the front or back for a good view of the city. Almost all Metro and REM stations will allow you to get off and board in the other direction without passing through turnstiles.
As Typo Knig mentioned, we did a short visit to the Vieux Port area (lunch, then a ride on the wheel), then a jaunt over to the BioDome.
I’d love to visit again some time; we were there in 2017 and did the BioDome / botanical garden area, as well as wandering the Underground area with @EmilyG.
Gorgeous day, weatherwise (the last good day of the trip, actually; it rained every other day). The only bad part, as noted, was the traffic - rivalled DC-area rush-hour traffic, I kid you not (not helped by Google giving us rapidly-changing directions, and NOT telling us which way to go on one split).
Getting back to the border was mildly amusing as well. I had forgotten to check crossing hours at the various places, and my friend who was navigating couldn’t figure out which one we’d be going to. Luckily, we wound up at one that was open 24 hours. And, unlike the last few times, the border guard didn’t seem like she thought we were would-be criminals, just asked where we were all from, and if we’d bought anything. We declared the half-empty box of TimBits, and she waved us through.
Our AirBnB was roughly 65 miles from Montreal (just under 2 hours getting there, rather more getting back!!). A relatively easy day trip, all in all. The area we stayed in, there is quite literally nothing to do within a 90 minute drive, except for some hiking; any more local activities were all closed as it was too early in the season.
Traffic in Montreal can be brutal. A lot of people who live in or near the city centre don’t drive, or don’t drive much.
You should come back to Montreal sometime and we could meet up It’s a city with a lot to see. I love it, though I’m biased of course.