Politics shouldn't be brought into this. There are several inaccuracies in this post. First, Raonic was not born in Serbia, he was born in Montenegro as stated in the article. Second, Canada did not bomb Serbia or any other part of the former Yugoslavia - NATO did. Third, the International Court of Justice dismissed a complaint against NATO and the 10 countries that operated under the NATO banner on the grounds that this was a humanitarian intervention. One presumes that if Rwanda filed suit against the United Nations for actions taken by UN Peace Keepers from Canada, the same result would have occurred.
With regard to why Raonic is Canadian, according to Census Canada, in 2011, 6,775,800 Canadians were born outside of Canada. They became Canadians through a process called Naturalization. This was 20.6% (over 1 in 5) of Canada's population, up from 19.6% in 2006. Raonic is one of these individuals.