In 2008, Christian Vande Velde was a sensation at the Tour de France, especially in the mountains. Hailing from Lemont IL, it almost didn't make sense that he thrive in the high alpine environment, yet there he was with the best of 'em. Asked by a sportscaster how he learned to climb, despite the flat geography of his rearing, he said he would seek out any and every steep pitch, and repeated ascending them until it equaled the distance of a European col. That makes sense- make do with what you have. Armed with this little tidbit of motivation, living in metro Toronto does present some workouts for the aspiring mountain goat.
My favourite urban hill climbing circuit consists of five hills in the Don Valley, with each circuit taking ~30 minutes. This is a great ride for cyclists stuck in the city looking for fluff-free rides, and is best ridden in the morning before work, in the evening, or even during a lunchtime break (if your schedule allows).
There's several variations to this route, but here's how I do it: starting from Yonge & Aylmer, get the legs spinning quickly down Rosedale Valley Road, and then turn north on the Bayview Extension. With Pottery Road approaching, it's now time to bring your climbing legs out. Make a right onto Pottery (600m, 5% avg grade), and keep it in the big ring. This stretch was repaved last year, so it's now super smooth, with sharrows on the descent, too. When you get to the top, go back down and climb it one more time. Very good. At the top of Pottery, make a left, and spin a light gear for your couple minutes on Broadview.
After Broadview turns 90° to the right, go left onto the first residential street, called Beechwood Drive. This is your next climb (500m, 6.8% avg). Beechwood is a one-way residential street at the top, but its essentially empty, only used as access to a Toronto Police dog training facility at the bottom. Climb Beechwood twice, again in the big ring. It's a very steady grade.
Now reverse the route back across Broadview, and down Pottery, all the while spinning your legs out in an easy gear. When Pottery bottoms out at Bayview, you know what to do- climb. The Bayview Extension (1.3km, 3.9% avg) is best done only once, and on the wide shoulder, since it's heavily trafficked, even for my standards. Big ring it. The pitch of the road has slight gradation changes, but when it flattens out before the railway bridge, that's your chance for a brief breather before kicking it out of the saddle for the last, tougher 100m.
At the top, go straight into the Loblaws parking lot, and make a right onto Moore Avenue. Spin easily all the way across Moore (which changes names to Southvale Drive), until it ends at Millwood Drive. Turn right onto Millwood, and then your first right after that, called Redway Road. This road loops around another grocery store, but when you see a sign for an access road to the North Toronto Water Treatment Plant, what's down below is the steepest climb in the city (300m, 9.7% avg). Hopefully there's something left in the tank, because this one brings you close to 'empty'. It's OK to climb this in any gear you like, but at least do it twice. Even if you're really fit, this one will make you gasp for air.
Now that the workout is almost done, reverse your route across Millwood, and down the Bayview Extension, all the while restoring some speed in your legs. Shoot down Bayview, and go right onto Rosedale Valley Road (2km, 1.2% avg), which has a gentle rise to it, except from the stop sign in Rosedale until you hit Yonge again, which is a bit steeper. You know you're going good if you can ride Rosedale Valley Road back in the big ring, with a high cadence.
While this may, or may not prepare you for the European cols, it does tie in most climbs to be found in the urban core. I like doing this ride once or twice a week, just to log some quality time in the saddle, and I find it helps my endurance for some longer weekend rides.