I think they are very comparable, but I do feel like UM's D is actually slightly stronger. They have given up only 184.0 ypg compared to 247.4 for NU. Also the one stat (scoring defense) that has been touted in NU's favor is actually slightly off (7.0 ppg for NU vs 7.6 for UM). The number for UM includes a pick six. The UM
defense has actually given up
less ppg than NU defense (6.2 ppg).
Regarding strength of schedule, here are some commonly used metrics:
Sagarin --
UM 70.76 (31) ; NU 67.76 (56)
FEI --
UM .226 (41) ; NU .278 (52)
S&P+ -- UM -0.3 (81) ;
NU 0.2 (55)
So 2/3 metrics give Michigan the edge SOS wise. The one that doesn't, S&P has Michigan ranked at #3 overall in total S&P and NU at #29 overall, so I'm not sure you want to trust that one
I'll be at the game this weekend and I wouldn't be surprised if NU won the game (especially after the BS UM has pulled the last few years), but I do feel that UM defense has the upper hand, especially at home.