In Chicago it may depend on which form of transportation that you're riding. On the Metra, it's second nature to see laptops, tablets, kindles, etc. On the El, coworkers have shared that tablets aren't as common (mentioning theft) and people can be apprehensive to flashing their smartphone. I'm aware that's a major blanket statement but my experience is that ride duration, available seating, and rider demographics play a role.

Toronto reporting... iPads and tablets on the subway are 100% normal and unremarkable here.