The best list of links for Croatia (and many other European countries) are posted on the Federation of East European Family History Societies website.
Here are a few recommendations for beginning Croatian genealogy and family history research.
Getting Started with Croatia Research, FamilySearch: https://www.familysearch.org/learn/wiki/en/Croatia
A Guide to Croatian Genealogy, FEEFHS: http://www.feefhs.org/links/Croatia/cghs-gcg.html
Croatian Research at the Family History Library by Thomas K. Edlund, FEEFHS: http://www.feefhs.org/links/Croatia/croatian-fhl.html
Croatian State Archives, some searchable databases: http://zagreb.arhiv.hr/en/index.html
Croatia In English, for those speaking English tracing their Croatian families and/or planning to travel to Croatia: http://www.croatia-in-english.com/
Curkovic.ca by Ivan Ćurković: http://www.curkovic.ca
100 Years in America: http://100inamerica.blogspot.ca
AT THE BCGS LIBRARY
We have a number of books relating to Croatia including The Croatian Immigrants in America by George J. Prpic. [BCGS 947.0 PRP] This has good information on emigration from Croatia and an excellent bibliography – with newspapers and journals as well as articles and books. It does include references to Canada as well as the USA.