Emirates and Delta are both in T4 at JFK, but Delta also offers flights from T2, which requires a trip on the Jitney which takes several minutes (or the AirTrain). You'll have to clear US immigration and re-clear through security. Delta's minimum connection time on a international-to-domestic ticket at JFK is one hour and 45 minutes, and you're trying to do this in one hour. Presuming that you're doing this on separate tickets, I would strongly recommend that you not book these flights. There's a very good chance -- if not a guarantee -- you'll miss your JFK-YUL flight.