Can I use cedar mulch around these plants? Will creosote be an issue?
Yes, mulching is a good idea. It helps the soil retain moisture, reduces weeds, moderates soil temperature and eventually adds organic matter. I recommend you put down a layer of compost first, to add nutrients and then the layer of mulch (no more than 2 inches and not right up against the trunks / stems).
Creosote is a product that is added to railway ties and utility poles to act as a wood preservative. It is most unlikely that it would found in the cedar mulch you buy at garden centres, so I would not be concerned about this material.
However, depending on the source of shredded cedar, there is a slight risk of it carrying Cedar Apple Rust disease. On the other hand, the disease spores for that can just as easily come from a nearby cedar and most Toronto neighbourhoods have some.
Therefore, I would go ahead and mulch.