How far north do tropical airmasses (dewpoints in excess of 70 degrees) go into Canada?

Occassionally in the summertime, warm fronts, bringing dewpoints in the 70's will "surge" northward into the Northern United States. Every few days, for example, Chicago will see dewpoints inthe 70's, along with Green Bay, and sometimes even into the U.P. of Michigan. On weather maps, I never see warm fronts more than 200 or so miles north of the Canada border, but I also know US weather maps do not forecast for Canada - especially in areas where no one lives - very few people live 300 miles North of Marquette or Caribou. Do tropical airmasses ever reach Churchill, how about Igaligut (capital of Nunagut)? I do know that hot temperatures will occassionally reach Alaska, latitudes of 70 degrees or ever higher, but I never see HOT airmasses going over 55 degrees in Central Canada. Why is this?