You could narrow this topic by answering a series of open-ended questions concerning "adult literacy in Canada." Obviously your teacher wants you to organize your thought in a web map - which is easy once you have some answers. Consider the following questions:
- what are the adult literacy rates in Canada?
- have these improved or worsened in the last 10-25 years?
- what are the implications of this change (or lack of change)?
- How has adult literacy (whether high or low) affected Canadian economics? (number of employed vs. unemployed, types of jobs most prevalent in Canada, Canada's economy compared to the rest of the world's economy)
- How has adult literacy affected social change in Canada? (Are people's interests reflected by the literacy rate, and if so, how?)
- How have YOU been affected by Canada's adult literacy rate?
It seems this topic lends itself to looking at adult literacy as either unusually high or unusually low. Either extreme would cause change in each of these areas. After researching a little in all three, figure out which one has the most research to support it and dig into that one a little deeper. Otherwise I fear your topic is still too broad.