To get the AIA you have to catch the City ferry at the foot of Bay Street @ Queens Quay. Take the ferry to Wards Island.  Then walk to the main road and walk to your right or west to the first bridge. Go over the Bridge and walk straight to the dead end at the Harbour.  Turn left and proceed to the end of the walk.  You are now at the AIA.    This is approximately a 15 minute walk.

Here is a link to the Toronto Island Ferry Schedule.