I have cc'd this message to Francis Zwiers, who is the Canadian Govt scientist (at Victoria) you might like to contact for further info. He was involved in a project to adjust Canadian temperature data for many of the problems of site changes and observational practice changes that have occurred over the years. For Canada, we have incorporated this dataset. We try to include as much of this work as possible, but for a lot of countries we have to do this work ourselves. This is sub-optimal as we don't have all the necessary metadata (data about data), but we do the best we can.