According to authoritative websites I've seen, the best grass seed for
places with severe winters like here in Ontario is a mix of bluegrass and
fescue. Last summer I needed to patch a couple of areas in my lawn so I
bought a mix at a local garden centre (which generally sells good products)
labelled "Canada no. 1 lawn seed", boasting 40% Kentucky bluegrass, 30%
creeping red fescue, and 30% perennial ryegrass.

It came up fine. I had some left over so I used the remainder in April to
seed a couple of areas that were damaged by landscaping late last fall.
These new areas are also germinating fine.

But the areas I seeded last summer are almost completely dead. It's been
warm enough the past week that if they have any life they should be
sprouting by now (the established lawn all around them is almost ready to
cut). If this grass isn't going to last over winter, I'm not sure if I
should even continue watering the newly-seeded areas, or dig them under and
start again. And if a bluegrass/fescue mix can't survive, what can I use for
new seed?

The ironic thing is that for most of the past 22 years I've lived here I've
used cheaper brand-name seed bought at the local hardware store and have
never had this kind of winter damage.

It came up fine. I had some left over so I used the remainder in April to
seed a couple of areas that were damaged by landscaping late last fall.
These new areas are also germinating fine.

Wild guess: the ryegrass established, the other two species didn't.
I'd overseed with just bluegrass and red fescue, and keep watering.

Kay