It's a bit of a stereotype in Vietnam that people in the North are discreet and conservative while people in the South are direct and fun-loving.
From traveling both to Hanoi and Saigon a few times, I would say it's kinda true. I mean I was getting more offers for threesomes in Saigon than I have in many other places including Bangkok, Europe or the Sates.
That said, there are plenty of guys on apps like Grindr, Hornet and Blued in Hanoi. Not sure about your age/body, but I don't think you should have problems finding available guy.

As for accommodation, I would recommend Airbnb, if you plan to bring guys over. In the best case, the hotel will make the local guy check-in and show his ID. In some places, you even have to pay an extra fee or the guest might be forbidden from going to your room, though I haven't heard of the latter happening.
I know some guys, especially in Hanoi, hate meetings people in hotels because they have to go through check-in and face the looks of the hotel receptionist.
The good thing is, plenty of Airbnb places in Hanoi, don't have a doorman, so guys can walk in straight to your apartment.

Funny note: the guys are not only supposed to check-in but also check-out at the reception when they leave. However, not many do that. I remember one time, when I stayed around one week in Saigon, at the moment I was about to check-out from my hotel, I was informed that the number of guys still showing up as checked-in in my room was in double-digits Luckily, no extra charge.
Another time, the reception actually called me to come pick up the guy and mentioned in front of him that there were already 3 people that have checked-in in my room. The guy was a bit surprised, but he still performed pretty well.
So, definitely an Airbnb is the way to go!