Searching for Alexander family roots

My grandfather was named William Alexander.  He lived with his uncle in county Armagh, but I believe he had at least 2 sisters, who lived with their parents.  My father, James Alexander was born June 27, 1924 in Londonderry.  William married Ellen Byrne April 7, 1924 in Castlefin , Co Donegal..  William sailed for Canada shortly after their marriage, and Ellen and baby James sailed 3 weeks after James was born for Canada.

I am looking for any information on William Alexander, and his parents/siblings.  Would love to find out about ancestors, and any living relatives.

Thank you for your help!

I believe I have seen the marriage certificate of William and Ellen.  On that certificate, William's father was listed as James Alexander.  I was told that William lived in Co Armagh with his Uncle, but I have no name for this person.  I was lead to believe that William could have been born in 1885.

Thanks again!