Software for scanning slides

I am digitalizing old 35mm color slides. Some of these are slightly underexposed due to camera failure, while others--I shot into the light so faces are rather dark. Looking at the slide, I can see people's faces; details are clear. However when I scan them in, the photos come out dark. Do you recommend any software to use with a Canon scanner so these photos will be very close to the original slides?

I realize I can make adjustments post scanning in the program, but heard it was better to have a good scan in the beginning which made later adjustments easier. Thank you.