The big first question to ask, is there a seperate entrance to the basement? The tenants need a safe point of egress if something were to happen in the house.
The basement bedroom windows will need to be large enough with a clear path for egress as well. (you can get the exact sizes from the city website)
Independent furnace and ductwork to each suite.
Electrical needs to be able to handle the load from both suites.
smoke alarms through the house need to be interconnected as well as the carbon monoxide alarm.
Fire protection between suites and a few ceiling height restrictions.
Also I believe there needs to be enough parking stalls for both suites.
You can find more info on any of this on the city's website but that gives you an idea of what is required. They also explain what permits will need to be pulled and all that info.
The biggest pro is the huge increase of rent you can get. I mean what other renos can you do to a house for 40-60k that will get you $1000+ more in rent per month! It can turn a house that may just cashflow into a house which cash flows $500+ a month. It is also very unlikely that both suites will become vacant at the same time so it gives you that added security.