@cr7isthegoat had a previous appointment booked back in Jan 2020 which kept postponing and in such cases they are considering the emergency appointment request if the families are seperated. Or else they are rejecting the emergency appointment.
So lets say, you get an appointment in May 2021 and you reach Canada and stuck here, your spouse is in Usa, if everything goes well and your appointment isn't cancelled well and good, or else if its getting cancelled and gets postponed indefinitely month after month then you can try requesting emergency appointment. Remember, if you book appointment today and request for emergency apptmnt a week or two weeks later they are going to straight away reject it. I faced this. So you need to atleast wait for 1 or 2months and give it a try. I also have my 2 cents, if you haven't reached Canada and try emergency apptmnt staying in Us they'll reject.