I generally agree with this, but I think that Canada may well end up *less* populated than OTL. Hard to say.
Indeed. Any deal that can defuse the ARW is going to leave the British North American colonies with a great deal of Dominion-like autonomy, which surely includes control over their immigration policy and dealing with the Indian tribes. This ensures that Dominion of North America is going to adopt the same immigration-friendly, native-busting, all-out expansion as OTL US. Not only the OTL US parts of it are going to grow at OTL speed, the Canadian parts are going to grow at OTL US speed, and even up considerably more populated than OTL. Moreover, if Britain is not focusing on India, the Western Hemisphere is going to become the focus of its empire-building efforts, with sizable chunks of the Spanish colonial empire ending in the American Dominion (Louisiana goes without saying).