Hrm, if you are after toning up, then I would recommend the yoga. Yoga is excellent for all those core muscles that keep everything in place

As far as the cycling goes, I'm not sure it'll do my for your tummy, although of course if you do
lots then you'll be burning a good few calories.
If you go into the "My Wii Fit Plus" section, you can create a workout based around your tummy, or indeed any other part of your body.