There are many ways to answer this question. The Boreal Shield, which compromises of 20% of the landmass of Canada and 22% of its fresh water is an incredibly important tract of land. Moreover the implication of this land in connection to acid rain are far reaching in many ways.
First, we need to ask where acid rain comes from. When we do this, we will discover that the smelting of metals and the usage of fossil fuels lead to acid rain. This is an important point to keep in mind, because Canada is known for its mines. So, to reduce acid rain, Canada's top industries will take a hit. From this point of view, the human economic system will be impacted by the Boreal Sheild.
Second, from ecological point of view, scientists are saying that due to acid rain, the trees of some area of the Boreal Sheild (Ontario and Quebec) are suffering. The implications can be far reaching, because trees effect the wildlife and other important things like oxygen. Trees also purify the air that we breathe.
Third, scientists are saying that the aquatic life is also being affected by acid rain. They state that certain places in the Boreal Shield have great sensitivity to pH levels. Hence, a shift in pH level can cause unforeseen problems with the aquatic life - another big industry of Canada.