Does Quebec coverage include Ottawa, ON?

No it doesn't. Ottawa is in Ontario, therefore it is not included in Quebec coverage zone.

It does include part of the Ottawa area, as long as you stay on videotron's towers. Turn roaming off on your phone if you want to be sure. As to extra charges, there will be no unhappy surprise on your fizx bill due to roaming charges because it is all prepaid. If you're out of zone, the phone simply won't work unless you have money in your fizx wallet, in which case that money will be used up by roaming and then the phone will stop working.