Vancouver is the warmest weather city in mainland Canada (it's island neighbor Victoria technically wins) so not too cold and barely any snow, but what Vancouver has is the rain 8 months of the year. I have lived in both Vancouver and Northern CA and would probably also counsel you to choose UBC. Life there for grad students is great, the city really can't be beat, and job opportunities (not to mention your eventual retirement): pensions, healthcare) will probably be better.
In addition, Davis will be hard to navigate (or at least to leave, and believe me, you will want to leave) without a car, whereas Vancouver is (in my opinion) one of the most accessible cities in North America.
Just my $0.02 since I've lived in both areas! Feel free to PM me if you need more details.