Oh dear
This looks a bit like looking in a haystack for a needle that may not be there to start with.
Not all baptisms and marriages made it into the Church of Scotland parish registers, and not all the records that were made have survived. So there may not actually be any record to find.
I assum that you have checked all possible leads at
www.scotlandspeople.gov.uk including the Roman Catholic baptisms and marriages.
There are some registers of other denominations, but these are generally not available online. On the one hand there are all the assorted minor presybterian churches, sometimes referred to as Secession churches. Most of the extant records of these churches are held in the National Records of Scotland, but they have to be consulted there. However very few of these date from far enough back to include the marriage, let alone the baptism, of your Adam Sutherland. The only ones old enough and extant would be from the Associate Synod (1733), Burgher (1747), Antiburgher or General Associate Synod (1747) and Relief (1761) churches, and a few Reformed Presbyterian and United Presbyterian records dating from the mid-18c century. You would need to know where to look geographically to use these records, or plan to spend a very long time peering at screens.
Another possibility is records of the Episcopal Church. However these are hard to find because they are not held centrally; some are in local archives, some in diocesan archives and some in the individual churches. So you really have to know where to look, and without knowing where Adam Sutherland came from it would be a huge task.
I note from the IGI that with a single exception all the Adam Sutherlands baptised before 1800 were baptised in one of the northern counties - Shetland, Orkney, Caithness, Sutherland, Aberdeenshire. The exception is one baptised in Edinburgh in 1769, which is far too late to be a husband and father in 1784*, and to be the one who died in 1807, assuming that they are one and the same, which does seem likely.
*Theoretically he could have married at 14, in 1783, and fathered a child born in 1784, but in practice boys didn't marry as young as that because they had to be able to support a wife and family before they could consider marriage. Also, assuming that you have arrived at 1784 by subtracting Elizabeth's age at death from 1860, then depending on when she died in 1860, she could have been born in 1783. And that assumes that her age on her death certificate is accurate. If the informant didn't know the surname of Elizabeth's mother, can (s)he be relied on to know Elizabeth's age correctly?
This Adam, born 1769, is the son of a John Sutherland and Agnes Semple.
Speculating wildly, I wonder if this John Sutherland could be a brother of your Adam? Might just be worth a look. I note that John S and Agnes Semple were married in 1762 and had a daughter Jean in 1764 and a daughter Janet in 1767, then John in 1769.
On the other hand, I note that an Adam Sutherland and Janet Fraser had a son Alexander in Aberdeen in 1781.
More speculation: could this be an older brother of your Elizabeth, his parents then moving to Edinburgh before Elizabeth's birth? (Does the 1851 census actually say that Elizabeth was born in Canongate?) It might be interesting to see what that Adam's occupation was.
