Cascade lodge (through Worldmark) only offers 1 bedroom units, while Sundance has 1-3 bedroom units.
Cascade lodge is very near the village, so it's possible to walk to all the shopping, groceries and restaurants easily. Also, it has a large heated pool (one of the largest in Whistler) and a few hot tubs (2 or 3? can't quite remember).
Most units at Cascade Lodge don't have a deck, it backs onto a thin strip of trees which separates the lodge from the highway and there aren't any bbqs.
Sundance lodge has larger units, it's built on the side of the mountain so there are fantastic views of the valley, mountains and lakes. The units all have large decks with bbqs and it's quite close to the creekside gondola. There is one shared hot tub for the complex.
Unfortunately, it's not very close to the village and it's a steep walk to the gondola. There is a small village (called Creekside Village) at the base of the creekside gondola. There is a nice grocery store, a few restaurants, a starbucks and a handful of stores. While this little village is comparable to the base village at many smaller resorts, it doesn't compare to Whistler village.
I'm not sure which resort has easier access to the lifts. From Cascade lodge it's quite a walk to the lifts. I would do the walk if I were snowboarding that day (snowboard boots are quite comfortable to walk in), but I definitely wouldn't walk that far in ski boots. It's only a 10 minutes walk, but mostly on pavement and/or paving stones. Unlike Sundance, the walk is flat and easy.
I've stayed at both lodges, but usually in the summer/fall. I prefer to ski at a different resort in BCs interior (Sun Peaks). My personal preference is Sundance lodge because it offers a view and a nice deck. We like to use the BBQ and we often invite friends/family to join us (cascade only has 1 bdrm units). However, Cascade is very convenient to the village and we LOVE Whistler village.