Where in Belfast are you staying? The city centre?
I lived in N Ireland for 3 years, and although there isn't a big natural appetite for Rugby League, neither is there an in-built anti-league policy unlike some union dominated places. I suppose that's because Union isn't actualy that massive there either.
Anyway back to the point... There are a few nice pubs in the city-centre which show Sky Sports. The problem is that they will ALL show football ahead of any other sport, be that League or Union so there's not much chance of getting your wish if the timings clash.
Don't wear any replica shirts as I think they are banned in most places as they typically represent sectarianism of one sort or another (certainly don't wear a Rangers or Celtic shirt!!!)... however it's a nice friendly city-centre and I'm sure that most places will be glad to help if they can accommodate your request.
Try the Crown Liquor Saloon opposite the Europa hotel, that's quite nice, or McGraths (google it). There's also a nice place next to the car park of the Castle Court shopping centre, and Rockie's sports bar is in the Odyssey complex in the titanic quarter.
The best bet is to start at City Hall and work your way outwards... however don't venture into the suburbs - they're safe enough but there's still the odd narrow-minded eejit (from both sides of the fence) who might spout off at you once he's had a few pints of Harp or Tennants.
Good Luck.
