and are mosquito vectors of more than 22 arboviruses that infect humans. Our objective was to develop regional ecological niche models for and in the conterminous United States and Canada with current observed and simulated climate and land-use data using boosted regression trees (BRTs). We used BRTs to assess climatic suitability for and mosquitoes in Canada and the United States under current and future projected climates. Models for both species were mostly influenced by minimum daily temperature and demonstrated high accuracy for predicting their geographic ranges under the current climate. The northward range expansion of suitable niches for both species was projected under future climate models. Much of the United States and parts of southern Canada are projected to be suitable for both species by 2100, with projected to expand its range north earlier this century and further north than . Our projections suggest that the suitable ecological niche for will expand with climate change in Canada and the United States, thus increasing the risk of -transmitted arboviruses. Increased surveillance for these vectors and the pathogens they carry would be prudent. https://doi.org/10.1289/EHP5899.