Which Canadian province is most socially conservative?

[King of Kensington]

Very true.  The Maritimes have strong historic links to New England.  At the time of Confederation they were certainly stronger than they were to central Canada (and even today, many Maritimers see Boston as the "big city"). 

The Maritimes is part of country's poorest region (along with Newfoundland) and in some ways it's a bit New England meets the South (lots of Baptists, rural Black communities in Nova Scotia, etc.)

Northern Maine does resemble New Brunswick in a lot of ways, though most of Maine's population is in the southern part of the state that is more oriented towards Boston.

(I know Maritimes doesn't include Newfoundland, which is also poor and more religious, though it's less linked to New England.)

[King of Kensington]

I posted all census agglomerations that are at least 20% evangelical in another thread.  I had forgotten to include Newfoundland and list again:

Steinbach MB  63.5% (Provencher)
Leamington ON  31.7% (Chatham-Kent-Essex)
Lacombe AB  31.7% (Wetaskiwin)
Kentville NS  31.3% (Kings-Hants)
Grand Falls-Windsor NF 31% (Bonavista-Gander-Grand Falls-Windsor)
Abbotsford BC  28.3% (Abbotsford)
Chilliwack BC  28.3% (Chilliwack-Fraser Canyon)
Swift Current SK  26.3% (Cypress Hill-Grasslands)
Fredericton NB 24.4% (Fredericton)
Norfolk ON  21.6% (Haldimand-Norfolk)
High River AB  21.6% (Macleod)
Sylvan Lake AB  20.9% (Red Deer)
Brooks AB  20.8% (Medicine Hat)
Lethbridge AB  20.8% (Lethbridge)
Truro NS  20.6% (Cumberland-Colchester-Musqudoboit Valley)
Chatham-Kent ON  20.2% (Chatham-Kent-Essex)
Wetaskiwin AB  20.2% (Wetaskiwin)
Red Deer AB  20.1% (Red Deer)
Salmon Arm BC  20.0% (Okanagan-Shuswap)

The evangelical Protestant population in Newfoundland is mostly Salvation Army and Pentecostal, and it's heavily concentrated around Grand Falls-Windsor.

[🐒Gods of Prosperity🔱🐲💸]

Attendance at religious services by province and regional pockets, albeit from 2003:

http://www.ghcisocialscience.com/uploads/1/3/5/9/13590293/religious_attendance_in_canada.pdf

BC and Quebec are the lowest; PEI, New Brunswick and Newfoundland are the highest.

"Bible belts" are evident in Atlantic Canada and the rural southern prairies in particular. 

PEI has the highest figure there by province for monthly attendance (53%) which is close to the US average.