Charles Edward Poulett Thomson Baron Sydenham 1799-1841
Thomson, a British businessman and politician, was sent to North America to implement the Union of the Canadas. Having won assent for the union in 1840, he was elevated to the peerage and served as the new province's Governor-General until his untimely death in Kingston. In establishing a system based on harmony between legislative and executive branches, yet one which fell short of responsible government, he succeeded in bringing together moderates in an administration designed to aid in recovery from the recent political, social and economic troubles that culminated in the Rebellions of 1837-38.
Plaque via Alan L. Brown's site Ontario Plaques. Full page here.