I'm looking for information on my great great grandfather, a Frank Kaslawska (or Kaslowski?) who may have been from Warsaw, Poland, and might have later lived in the area of Trembowla. I don't have any concrete information on him and only one document that mentions him, his daughter's marriage certificate from Ontario, Canada, which lists his name as Frank Kaslawska and lists the mother of his child as Mary Kasky. A cousin states he was born in Warsaw sometime in the 1860's or 70's and a great aunt states he died in Dachau camp in 1941 (don't know what year he would have entered in at, though he would have been elderly).
I'm having a hard time finding anything at all in terms of actual records referencing him, aside from that one Canadian marriage record where he is listed as a father of the bride. I know his daughter was born in Trembowla in 1899 and that his wife was also from the area. I am unsure, though, which countries records I should be searching as that area seems to have switched control various times over the years he could have possibly been there.
If anyone could point me in the right direction of where to search, I'd appreciate it.