This book details the development of eleven modal auxiliaries in late 18th- and 19th-century Canadian English in a framework of new-dialect formation. The study assesses features of the modal auxiliaries, tracing influences to British and American input varieties, parallel developments, or Canadian innovations. The findings are based on the Corpus of Early Ontario English, pre-Confederation Section, the first electronic corpus of early Canadian English. The data, which are drawn from newspapers, diaries and letters, include original transcriptions from manuscript sources and texts from semi-literate writers. While the overall results are generally coherent with new-dialect formation theory, the Ontarian context suggests a number of adaptations to the current model. In addition to its general Late Modern English focus, New-Dialect Formation in Canada traces changes in epistemic modal functions up to the present day, offering answers to the loss of root uses in the central modals. By comparing Canadian with British and American data, important theoretical insights on the origins of the variety are gained. The study offers a sociohistorical perspective on a still understudied variety of North American English by combining language-internal features with settlement history in this first monograph-length, diachronic treatment of Canadian English in real time.