You can write directly to the church Immaculee Conception in St-Ours, they may give you some info but i'm not sure if they can provide the birth certificate to a "stranger".
Also, you can trythe "Archeveche Of Montreal", they should have pretty much everything concerning catholic people in Quebec.
Since 5-6 years, church do not provide anymore birth certificate.It's now all canadian government responsability to do so.
And by the way, i come from the city of Sorel/Tracy, province of Quebec, Canada. There are so much Peloquin living there, you won't believe it.There is a lot of small town aroud like St-Pierre-de-Sorel, St-joseph-de-Sorel, St-Ours, Ste-Victoire (a lot of Peloquin come from there) all within a mile from Sorel.