Wait until you won't be crossing the paths of any cars, then go.
Here's the thing, though. Do not, for one second, expect any drivers to slow down because you're in the road. They go about their business, you go about yours, and everyone gets where he or she is going. It's remarkably efficient, but it depends on both driver and pedestrian having nerves of steel and, more importantly, on both of them understanding the rules.
People accustomed to crossing the road in Montreal can wreak havoc in other cities, especially Canadian ones, if they haul their habits with them. In Ottawa, Calgary, and Edmonton, for instance, drivers will often slow and even stop to let a jaywalker stopped on the yellow line pass in safety. (In Toronto and Vancouver, they'll honk and glare and whiz by, but only if it's safe to do so; in Montreal, a pedestrian in mid-street would stand a small but non-zero chance of getting hit.) A pedestrian used to the kamikaze rules in Montreal will be thrown off his metaphorical stride by this unexpected politesse, and complex hand signals might well be required before he understands that the driver simply won't go until he's safely on the sidewalk.
A few years ago, the City of Montreal tried a public-education campaign featuring small children in a parent's arms or clutching a parent's hand and asking, something like, "Papa? Pourquoi on n'a pas traversé au coin?" ("Dad, why didn't we cross at the corner?") It was laughable.