First of all Vancouver is wet. Very wet. Especially if you ride through the winter. This can make it hard to have a single bike to do everything without some serious maintenance to get it race ready. As such, if you went with one bike, I would make sure to budget some money for maintenance (e.g., chains, cables, brake pads bearings). This would make me incline to suggest a slightly less expensive bike which would be aluminum. If also want to 50 km commute year round you will need fenders. Typically aluminum frames will have fender mounts, but some carbon frames will have them as well. That said, fender mounts typically add cost to a carbon frame as they have to bond in aluminum pieces for the threads raising the cost and making it less likely to be found on an inexpensive bike.
All these caveats aside, I commute about 50 km a day and my daily commute bike is carbon. Why? Because I liked the way it pedalled, the fit was good, and it was possible to mount fenders on it. To me the most critical component for performance is not weight, but how the bike responds when pedalled aggressively. Well made carbon frames can can be tuned a bit more in the layup, but this is typically only done well in higher end frames as the layup process is labour intensive and therefore costly. With lower end carbon frames it is a gamble and aluminum is likely a better bet. Frames that pedal responsively, just make you want to ride harder. Frames that feel "dead" make kilometres feel physically longer and for some reason they always make me feel tired.
In terms of aluminum, Hydroforming has been a bit of a game changer lately for tuning the responsiveness of aluminum frames, which is why we are seeing a bit of a revival. In the past aluminum has had a bit of a bad rap due to older aluminum frames which were often too stiff and could feel "dead" compared to a good carbon or steel bike. Now a well sorted aluminum bike can feel very similar to a more expensive carbon bike.
So where does that leave you? Basically, either could work depending on how it was built. If budget is a consideration, you are likely to get better bang for your buck with aluminum.
In terms of choosing a bike, I suggest the following workflow:
- Start with a budget;
- Determine what features you need for commuting (I recommend fender eyelets, some like panniers, but I am happy with a frame bag, seat bag, or front roll);
- Do you have to lock it up outside (if yes, avoid a carbon bike or any bike that looks expensive);
- Form a list of possible bikes;
- Got to your local bike shop and test ride; and
- Choose the one that gives you the biggest smile.
I would suggest avoiding online sales as these can only work when you know exactly what you want. Even then you are not likely to save much as complete bikes in Canada have a extra duty levied against them in addition to PST/HST taxes. Too many people get lured by a slightly better component spec, but most components work fine now so this is a bit of a false alure. Ironman is a long race (I know, I have done one), as long as your shifting is working, you probably won't notice any real performance difference. You will however notice a bike that doesn't fit right or one that you don't like the feel of... this is why test riding is critical.