I think there seems to be some confusion as to what is meant by Bible Belt. Bible Belt does not simply refer to number of religious people, it refers to number of Fundamentalists in the population. Total number of religious people is really not relevant here.
I did try to find statistics as to the percentage of Fundamentalists in each province, but was not able to. If somebody can dig up such statistics, it will be well worth looking at.
So we must consider indirect evidence. What are the issues that characterize the Bible Belt, or religious right? The issues are social issues, they are the red meat to Bible Belt. Issues such as abortion, homosexuality, death penalty etc. If a province has high proportion of religious right, if it is indeed the Bible Belt, we would expect that to be reflected in the attitude of that province towards social issues.
Homosexuality – The opposition to gay marriage was strongest and most fierce in Alberta. Indeed, Klein and Harper felt compelled to proclaim that they will erect a firewall around Alberta to keep gay marriage out. Alberta was also the last province to legalize gay marriage, it was dragged kicking and screaming into doing so.
Death penalty – I have already posted a poll about death penalty showing that support for death penalty is the highest in Alberta.
Abortion – I remember seeing polls which show that opposition for abortion is the highest in Alberta.
The only prominent Fundamentalist politician is Stockwell day, who is from Alberta. Now, a leader like that does not arise in a vacuum, there has to be plenty of activists, plenty of supporters for a leader to arise.
Taken it all together, there is plenty of evidence to suggest that Alberta is indeed the Bible Belt of Canada.