The marriage you're looking for is in the Shefford Co. marriage books (St. Joachim).
Ephrem Senecal, son of Ephrem Sececal & Euphrasie Leclair Joac 15-05-1865 Cusson, Luce.
For the same parents there are also marriages for a J.B. Senecal (1889) at Waterloo to Celina Davignon. In this one Ephrem Senecal is listed at St. Joachim.
Etienne Senecal (1873) at St. Joachim m. Melvina Gendrow.
Louis Senecal (1873) at St. Joachim m. Sephremie Gendrow.
Moise Senecal (1882) at St. Joachim m. Rosalie Serard
Luce Cusson's parents are listed as Michel & Lucie Desforges.
In the Granby marriage book (Notre Dame) Ephrem Senecal's marriage to Euphrasie Leclair is listed in 1844.
Ephrem Senecal, son of Etienne Senecal & Victorine Auclair (Notre Dame) 02-01-1844 to Auclair, Euphemie (at least I think this is the same person).
Her parents are listed as Louis Auclair & Josette Parent
You can find the Notre Dame of Granby and St. Joachim parish records on LDS microfilm.
Notre Dame de Granby (Shefford Co.)
1844-1877 LDS 1294724
1846-1870 LDS 1689489 Item 4
1871-1879 LDS 1689490 Item 1
1880-1899 LDS 1877568 Item 2
St. Joachim (Shefford Co.)
St-Joachim St. Joachim de Shefford
1860-1879 LDS1689493 Item 4
1880-1889 LDS 1877712 Item 2
1860-1877; index, 1860-1974 LDS1298633