Vancouver is mild, but Victoria (the Provincial capital, over on Vancouver Island) is far more mild than Vancouver. And it gets half the rain that Vancouver gets. (As for major Canadian cities though, Victoria is pretty small.)
I'm a fair-weather motorbike rider, and I've only missed about 3 days since April this year. I usually ride right through to November, but last year, I parked the bike for 'winter' at the beginning of December.
But yes, Vancouver gets a ton of rain, so if you don't like grey skies all the time, it can have a seriously negative effect on your mood. Outside of that, the winter months have very little in the way of daylight (~6hrs) while the summer months have a lot of daylight (~16+hrs). This makes winter hard for some.
My biggest issue with Vancouver was with parking. If you have a vehicle, it can be a difficult to a) find parking, especially in residential areas where parked is reserved for those that live in the area, and b) find parking that doesn't cost a small fortune anywhere near downtown.