In general, boggy soil should be good for all of them, unless maybe the clay is so heavy that there is not enough oxygen in it.

Fresh sawdust leaches nitrogen from the soil as it rots. So if you use it as a mulch, you should add some supplemental nitrogen to compensate for that. If you compost or let the sawdust rot before using it as a mulch, then it will improve the soil without first taking nitrogen from it. But to answer your question - it will not hurt cannas.

Just about any organic matter used as a mulch or added to the soil is good for the soil and good for the plants that grow in it. It improves the fertility of the soil and it also loosens it. If your clay soil is anaerobic, adding organic matter will make it more aerated, which will enable better root growth.