hmm, nope, not recorded as Joseph Rabastau on his marriage to Cécile, but as Joseph Vivien.
Ladouceur-27 is a woman, not a Joseph.
Joseph Lamadeleine dit Ladouceur married with Françoise Rouleau married her in 1777, she died in 1804 so not the right man.
Joseph Magdeleine, son of Jean Baptiste and Dorothée Brisebois, was born & baptized 16 Feb 1750 in Ste-Anne-de-Bellevue. https://www.genealogiequebec.com/Membership/LAFRANCE/acte/275534
Bapt IGD - Drouin (membership)
Joseph Lamadeleine son of same parents was born & bapt. 9 Feb 1752 in Ste-Anne-de-Bellevue
Joseph Eustache, son of same, born 15 Jul 1754 bapt. 16 Ste-Anne..; Eustache married Marie Louise Pilon in 1784
There is a Joseph Ladouceur who died 13 June 1809, buried 15th in Ste-Geneviève (Pierrefonds), given the age of 56 on the record, cited present Joseph Brisebois and Eustache Rouleau, no mention of relationship to anybody.
funeral image IGD ...
There is a Joseph Ladouceur husband of Marie Anne Pilon who dies 23 Jan 1846 buried 25th in St-Polycarpe , given the age of 78, not likely to be the one you are looking for. https://www.genealogiequebec.com/fr/LAFRANCE/carte/5602
The biggest problem is the wild variety of names they use, but on looking at the marriages I find for the children of Jean Baptiste and Dorothée, Eustache's marriage, there is no brother cited present named Joseph, just his father and brothers Pierre and Louis. He would have been old enough then to attend if living. Other brother Luc got married the same year, family wasn't around for it.