FWIW, it's not 'a data center'. It's at least 3 a few miles apart from each other. They might (probably do) still end up in Montreal, depending on where those city/county limits lie.
S3, Dynamo and some other servicea always have three AZs, sometimes they only expose 2 EC2 AZs to save money in new/small regions. James Hamilton just announced that they were going to stop doing this but I guess this region was already under construction.
Aurora requires 3 as well, in order to establish quorum for leader elections in case of network partitions.