Since both cities are highly contaminated with chemicals from mining and from toxic-waste disposal, I'd venture to guess that the result of driving there is that you will die a slow, painful death from poisoning.
Love Canal is not a city, it's a neighborhood of Niagara Falls, roughly 16 acres of the worst of which is fenced. Since the toxins have been buried probably nothing would happen unless you went digging around the soil and eating with dirty hands; or maybe spent a few years living in a tent above it.
I visited Centralia several years ago, and it was fascinating. I don't recall pedestrian access being impeded at the time, but there was definitely gas and smoke rising from a few spots around town. I happened to visit on a cloudy morning, and it had an eerie, ethereal feel to it.
There were several areas where the road was damaged, and it was clear that it wouldn't be wise to put too much weight over top, but there are still people living in the area.
