I Think that if Lana found out Clark and Lois were going to get married? She would be happy for him because she already knows her and Clark cannot ever be together again because she is full of Clarks weakness that ='s krytonite.
Plus she already told Clark in the Bride episode Season 8 Lana: Maybe Lana Lang and Clark Kent just weren't meant to end up together.
So She already knows each time they got together they were going against fate.
Clarks True Fate is with Lois Lane..
*Clois is Forever*
haha I know she would be happy but, what if she was like "What?" "Your getting married to the girl you used to call annoying and talked to much?" "Huh a lot must have happened when I was gone...." LOL I wanna c that now! :p