My wife and I flew down to Melbourne and went to the cricket on boxing day and as I tend to get sunburnt fairly easily I was a bit concerned about we were going to sit.
We were seated in M50 row AA and thankfully was in the shade all day, it was however a bit chilly with a bit of wind.
I would say any row from about row X backwoods in M50 remained in the shade all day.
Great view and the Sri Lankans were all out before tea, can't ask for more!
So if you're like me and not able to sit out in the sun all day but still want to experience a boxing day at the MCG, there are places where you can sit and not be in the sun all day.