May have taken place in Canada, but also elsewhere.
At least one child of this couple was born in Montreal (Quebec) Canada
Could be Ramsey instead of Ramsay.
her brothers William , Henry & John were married there
daughter Christina Mabel Smith, was born there too 4 Jul 1877
per Margaret Ramsay death certificate, she had been living in Ontario since about 1855
So, 1884 seems unlikely.
Leaves only possible date as 1886 for Agnes in Montreal.
Any explanation why a farmer & his family living in 1881 & 1891 in Plympton, Lambton, Ontario
will have a daughter born about 1886 in Montreal ?
I did not, until I read your post and decided to see what I could find. [I am not related, I just like to solve "genealogical puzzles"].
All I have comes from census & birth, death,.... , ...
Not knowing what you have, I may be duplicating your info.
I am not making much effort to sort what I have, sorry; and, most cases, I do not correct transcription - even though some are pretty bad.
I can send you images of acts, census,..., but only after Labor Day, when I will have full access to fast Internet.
Tell me what to send or not to send.
Still looking for their marriage, but all points to Ontario, not Quebec.
I am sure there is a lot more that can be easily found.
see my email. you can now remove your email address.