I believe that we have a better chance of suffering an EMP being detonated high over the centre of North America. That would both fry the power grid, and everything else electrical/electronic - which is pretty much everything.

Everything is still physically intact - and pretty much everybody is just fine.

Except that all the water treatment plants, hospitals, food & fuel supply chains, etc stop working for at least months, if not years. All the refrigerated food, in your fridge, stores and warehouses spoils.

Consider just the water treatment plants being out of commission for an extended period of time. How many people in just the GTA will suddenly have NO clean water? No clean drinking water, and no water at all for washing yourself, your clothes, flushing toilets, etc. Your car - and the gas pumps won't work - so you won't even be able to leave. Nowhere to go that's any better off, anyway.

What percentage of the population is still alive in 2 or 3 weeks?

Maybe 5 - 10%...