Y.O.Morales said:
1. Efficient means of transportation (something we lack here in PR; either you have a car or you dont move anywhere).
2. Relatively good climate. Maybe I can get accustomed to low temperatures. As for rain, that's not a problem because here in PR rains a lot.
Depending on the province, 50,000 to 100,000 is going to be your threshold for remotely decent public transit (ie. 7 days a week and transit past 6pm on Sundays). There are, I'm sure, a few exceptions but I'm not that aware of them. I only have in-depth knowledge of one province (BC) but I understand this is a pretty okay general rule.
Now, that stated, there is only one city in BC with transit past 12:30am seven days a week: Vancouver. Thanks to recent provincial government funding initiatives, BC now has a total of five cities with both universities and decent transit: Kelowna (100,000), Kamloops (80,000), Prince George (80,000), Victoria (330,000) and Greater Vancouver (2 million). I know that Vancouver, Victoria and Prince George all have sufficiently established universities that they should meet your needs. However, if you're also looking for a decent climate, you're probably limited just to Vancouver (UNiversity of BC, Simon Fraser University), Victoria (University of Victoria) and Kelowna (UBC - Okanagan campus).
Based on your current location and requirements for a decent climate with not too excessive a winter, your locations in BC are basically limited to Vancouver Island (Victoria is at the southern tip), the Lower Mainland (the area at the mouth of the Fraser River where Vancouver and its suburbs are situated) and the Okanagan Valley (Kelowna is at the centre). Anywhere else is going to have 3-5 months a year of snow on the ground and probably 3 months of temperatures below -10 celsius (14 farenheit).
3. I dont want a totally urban life. I'm sick of traffic jams and advertisement floods: ads, posters, banners, highway signs, neon signs, etc. Almost everywhere you look here in PR there's a Verizon, or Coca Cola, or Toyota ad crap. Seriously, someone who has lived here can tell you that the thing has broke its limits.
Well, in British Columbia, no billboards are permitted except in cities and on Indian reserves. Provincial law keeps them off highways except where the highway goes through expropriated Indian land.
That stated, it is pretty easy in any BC community to lead a semi-rural life, except in Vancouver. Like any other metropolitian area with 500,000+ residents, there is just too much suburb between the city and the country to be able to get the best of both worlds.
As for the rest of the country, I think that you're dealing with the same 3-5 months of snow 14 degrees or colder essentially anywhere you go in Saskatchewan, Manitoba, Quebec, the Territories and Newfoundland. I simply don't know enough about Nova Scotia, PEI and New Brunswick to say too much about the climate there. I understand that there are some favourable microclimates in Southern Alberta but cannot comment more. Hopefully, people who know about Calgary and Lethbridge (both of which have decent universities) can post.
The only parts of Ontario you might find habitable is along the north coast of Lake Ontario west of Oshawa or on the Canada-US border near Detroit. I think the climate probably rules out the rest of the province. (And even a short distance inland from these places yields a significantly colder climate). I don't think Toronto really fits the bill for you when it comes to non-urban life. I don't know the situation in Windsor Ontario but I think you may find it worth a look -- it's slightly warmer than Toronto. Although Kingston sounds otherwise absolutely ideal for you -- pretty, semi-rural, well-regarded university, it is too far east and basically has Montreal's climate.
So, my advice: find out what universities have programs for both you and your girlfriend. That will narrow things down pretty effectively. Then come back and ask us about the cities in which these universities are situated.