Same sort of question was asked recently on another thread.
Personally, as the weather forecast is, I think, reasonable, thinking of walking to OT from Manchester city centre and back and picking up the tram from Victoria home.
One tip is to go to Trafford Bar (the stop before OT), turning left on coming out, and walking down Talbot Road towards the cricket ground, and then turning right towards the football ground.
On returning, pick up the tram marked for Rochdale, as this uses the same line as the one for the cricket ground (Altrincham). This return will take you to Victoria rail station, but NOT Piccadilly rail station.
You could pick up the cricket ground tram at Trafford Bar as well if you're lucky to find one with room on, but, as stated, it's likely to be packed.

Are the trains back you mention from man utd stadium to wigan?

All trains are back to Deansgate / Oxford road / Piccadilly, where you'll have to change to get back to Wiggin However, there is just one direct service from Wallgate TO the stadium departing at 15.53 (arriving 16.41) The journeys are now finally showing on the National Rail Enquiries website. www.nationalrail.co.uk/ (The station code for the stadium is MUF)

All trains are back to Deansgate / Oxford road / Piccadilly, where you'll have to change to get back to Wiggin However, there is just one direct service from Wallgate TO the stadium departing at 15.53 (arriving 16.41) The journeys are now finally showing on the National Rail Enquiries website. www.nationalrail.co.uk/ (The station code for the stadium is MUF)

Quote ="tedglen"All trains are back to Deansgate / Oxford road / Piccadilly, where you'll have to change to get back to Wiggin However, there is just one direct service from Wallgate TO the stadium departing at 15.53 (arriving 16.41) The journeys are now finally showing on the National Rail Enquiries website. www.nationalrail.co.uk/ (The station code for the stadium is MUF)'" "A single to MUF please"

Quote ="tedglen"All trains are back to Deansgate / Oxford road / Piccadilly, where you'll have to change to get back to Wiggin However, there is just one direct service from Wallgate TO the stadium departing at 15.53 (arriving 16.41) The journeys are now finally showing on the National Rail Enquiries website. www.nationalrail.co.uk/ (The station code for the stadium is MUF)'" "A single to MUF please"

Shame you can't book them before the day

Myself and the missus will be turnout early and blagging it, I'm not really bothered if I have to walk on my hands all the way from Manchester City Centre to the ground to be honest!
I think a lot of people will just be blagging it on the day too, following the masses. that's what I've experienced in the past - so if you are a bit clueless, just look for the cherry & white shirts and follow them like me!