Looking for a cycling jacket for Fall/Spring
I also live in Ottawa, and the last week I've been wearing this MEC Cycling Jersey, along with another regular jersey and a cotton white T undershirt underneath.  This has been sufficiently warm for my 20 minute commute.  My arms get a bit cold, because they only have 1 layer, so I think I may pick up some arm warmers if it gets too much cooler, but I don't think it's really necessary. Other than that I don't have too many problems keeping myself warm.  I find that using lots of layers really helps to cut the wind, without compromising breath-ability.  As far as other clothing goes I have the Roubaix Tights which are worth every penny.  Have kept my legs toasty warm, while not making me sweaty, even in the cold (-1 degree C) we had this morning. Like the jacket that @geoffc mentioned, they have different material on the front and back.  The front blocks out the wind, and the back lets your legs breath and lets some of the heat out. Only problem I have is keeping my hands warm.