Tanya,I found the birth of David and siblings. Eliza and Catherine Tobin born:1 December 1889 Sydney Mines baptised:8 December 1889 Immaculate Conception,Sydney Mines,Cape Breton parents:John Tobin/Margaret Waugh
Nicholas Cornelius Tobin born:29 April 1891 Sydney Mines baptised:3 May 1891 Immaculate Conception,Sydney Mines,Cape Breton parents:John Tobin/Margaret
David Vincent Tobin born:5 December 1894 North Sydney baptised:29 December 1894 St Joseph's,North Sydney,Cape Breton parents:John Tobin/Margaret Waugh
Mary Ellen Tobin born:16 August 1902 North Sydney baptised:17 October 1902 St Joseph's,North Sydney,Cape Breton parents:John Tobin/Margaret Waugh
I also found this birth and think it may be your John Tobin and that perhaps he was married before he married Margaret Waugh.
Mary Josephine Tobin born:17 August 1885 North Sydney baptised:24 August 1885 Sacred Heart,Sydney,Cape Breton parents:John Tobin/Susan Hadden
These records were found on familysearch.org.I couldn't locate marriage certs for either marriage.What I would do is contact the Nova Scotia Vital Records office.They have an online website at http://www.gov.ns.ca/snsmr/access/vitalstats.asphttp://www.gov.ns.ca/snsmr/access/vitalstats.asp which may be helpful or contact the churches directly and explain what you are looking for.They can be very useful. As to the birth of John Tobin in Ireland I found 503.You would need other info to narrow this number down.If you find marriage certs it may have info to trace him in Ireland.Hope this helps,Kim