It isn't people who are below the poverty line; it's people who are at the tenth percentile in income distribution. That is, 10% of the population are below them and 90% are above them, in terms of their income.
If you look at that particular group.... This is from a research paper by Tim Smeeding. Your researchers probably know who he is already, but you may want to look at his international work. Using purchasing power parity numbers, he tried to compare the purchasing power in different countries. He concluded that the purchasing power--that tenth percentile--was about the same in the United States as in Europe. Canada was marginally above it--about 15% above it in terms of purchasing power.