Brenda,
You can use this link to see where the surname McCausland was found in Ireland in the mid 1800s:
https://www.johngrenham.com/surnames/
You’ll find it’s pretty well only found in Ulster. You haven’t said what denomination your ancestors were. That’s very important to know for searching church records.
Robert’s birth and marriage are long before the start of statutory birth registration (1864) and marriage registration (1845). To have much chance of finding him you need to know roughly where he lived and what exact denomination he was. Even then, not all churches have records for the period you need, and not all the surviving records are on-line.
I searched rootsireland for Robert’s birth marriage and the birth of any children to Robert & Mary, all without success. If you can find out (from Canadian sources) roughly where he lived, you could search the church records in PRONI (the public record office) in Belfast, but without some way of narrowing the search, it’s a needle in a haystack at the moment.
Possibly DNA testing may be a way of matching with others who have additional information about where the family originate. Family Tree DNA reportedly has more people with Ulster roots than any other company. That obviously increases the chances of finding a match. You might want to try them or, if you have already tested, you can transfer your results to them for no fee.
The North of Ireland Family History Society is running an Ulster DNA project in conjunction with Family Tree DNA and can offer testing kits at a reduced price. http://www.nifhs.org (Go to DNA project on the website). You don’t need to be a member of the NIFHS to participate in the DNA project.
