The advice given about the 401 across Toronto has been good, I'll add a couple of comments as we cross from west to east frequently to visit our daughter and her family. Mid morning to mid afternoon is probably the best time to cross avoiding the rush hours and giving some time for the accidents to clear. Staying in the curb lane (third lane from the left) of the express lanes eliminates the need to change lanes going across, In Ontario we have a number of "middle lane bandits" who sit in the middle lane and go slowly, sometimes you can make better time in the curb lane.
Also, Ontario requires all tractor-trailers (including US trucks) to be speed governed to about 105 km. (somewhere around 65MPH) so you will see lots of nose to tail truckers and some "racers going nowhere" between trucks in the curb and middle lanes. It was supposed to improve safety but it may be more dangerous than before!