I'm not sure if these reasons stand up.
Ontario and Quebec are only 16% and 5% nonreligious, and yet are generally perceived to be more liberal than Alberta. These numbers were from the Wikipedia (and thus not necessarily from the same study), so I checked out Statistics Canada - the 2001 census numbers on religion back this up (10 years old, but they seem to only account for religion every second census): Albertans are less likely to be religious than Canadians from any other province except British Columbia, and not insignificantly so.
In terms of urban population, according to the 2006 census roughly 64% of the province's population lives in either Metro Calgary or Metro Edmonton: a much greater ratio living in a large urban center than, say, New Brunswick, which is also perceived to be more liberal.
I don't know what evidence there is that correlates being English and/or white with being conservative, but even if true there is a significantly larger proportion of visible minorities in Alberta than in the Maritimes - and I'd wager a larger proportion of non-English speakers goes along with that.
Personally I don't think demographics has so much to do with it. I do think people in Alberta are suspicious of the Liberal party's motives, especially given their history. It's easy for one to say that the NEP is ancient history, but there are plenty of people in the province who remember it and are very vocal about it. It's hard to blame them, since many people lost jobs and businesses because of it. The NEP has become almost legendary here, whether a person feels that's justified or not. Chretien's Liberals didn't help as they played the different regions against each other (very successfully) - and Alberta always seemed to be the "bad guy". This led people here to feel that the province was not respected, and reinforced the notion that the Liberal party could not be trusted.
A lot of people in Alberta fear the Liberals and what they may do (again) to the provincial economy.
It's easy to assume that the province is conservative because it's supposedly full of white religious nutjobs, but I think the real explanation comes down to economics and history.