Good point. If you don't have good lights you could also hit an elk or something in the dark.

It's not really cycletouring if you do it at night. The self-respecting tourist should do it during daylight hours. I have done it at night in the winter because the days are so short and nothing is open. The Parkway is also a through-route to Banff and Jasper so I have done it in the dark because I had to get somewhere and I was never a good tourist in the first place. The Parkway is also a brevet route so you may have to do it in the dark.