Sydenham succeeded Lord Durham as Governor General of Canada in 1839. He was responsible for implementing the Union Act in 1840, uniting Upper Canada and Lower Canada as the Province of Canada. Upper Canadians were given a choice in the matter, which they accepted; Lower Canada had no say, and as a result many French Canadians were opposed to both the union and Sydenham himself. Sydenham was just as anti-French as Durham had been, and he encouraged British immigration to make the French Canadian population less significant. French Canadians referred to him as le poulet, "the chicken." Realizing he had almost no support in Lower Canada (now Canada East), he reorganized ridings to give the English population more votes, and in areas where that was unfeasible, he allowed English mobs to beat up French candidates. Louis-Hippolyte Lafontaine was one such candidate who suffered from Sydenham's influence; Lafontaine eventually left Canada East to work with Robert Baldwin in creating a fairer union for both sides.
Sydenham also settled the Protestant land dispute in Upper Canada (now Canada West), which the Family Compact had interpreted to refer only to the Anglican Church. Sydenham declared that half of the land set aside for Protestant churches would be shared between Anglicans and Presbyterians, and the other half would be shared between the other Protestant denominations.
Sydenham wanted to make Canada more financially independent, so that there would less danger of annexation by the United States. He had been working on this policy throughout the 1830s, when he was President of the Board of Trade in Britain, though he had little time to implement any economic reforms once arrived was in Canada. After less than two years as Governor-General, Sydenham died in 1841.
| Preceded by: The Earl of Durham | Governor General of Canada | Followed by: Sir Charles Bagot |
| Preceded by: New Creation | Baron Sydenham | Followed by: Extinct |