Sorry for the late reply, assessments were taking over. D:
So maybe you could evaluate his role in preventing the persecution of Jews during World War II (therefore, it is forcing you to make an argument and judgement when you're evaluating his significance in the situation). If this angle doesn't work out also looking at his Liturgical Reforms would be quite interesting to undertake for the History Extension project. Other than the Internet, Library (I know there is a virtual Jewish Library on the Internet somewhere, but can't seem to recall the actual URL address) I really couldn't recommend any sources. You might have to ask your teacher, but see if you are able to get access to some Magazines and Newspapers dating from World War II; I know that both the Time Magazine and the New York Times published articles which were highly controversial to Pius. Getting access to those articles would be fantastic for your investigation; as they are primary and wham a tonne of controversy into your Major work. They might even be on the internet somewhere.
My school does this 'SWOT' analysis activity in a number of social science subjects and History subjects. Basically the acronym stands for "Strengths - Weaknesses - Opportunities - Threats"; so that by evaluating the significance, impact or contribution of an individual would encompass all information. Therefore, I would make brief reference to his early life; such as his opportunies which therefore led to his personal beliefs. However, don't let the narrative take over your Major Work.
Best of Luck with your History Extension Major Work. Again apologies for the late reply, I wish you all the best. n_n