Didn't xtracycle change their bags/wideloaders at some point? I think there is an early and new style. Not sure. If the Sun uses the "original" style, in other words discontinued style, might be a problem. Likely still available now but down the line maybe not so much. I'll have to look into this further, I might be mistaken.

EDIT: Looks like it's no big deal, there is apparently a retrofit kit so that new style can be used on old style bikes.