Cairns came fourth in her K1 (one-person kayak) 500 metre heat Thursday.
Similarly, Tuva'a Clifton earned the quota place for Samoa after coming third in his K1 200 metre heat Saturday.
A fifth-placed finish in the semifinal put Clifton in the overall B Final, where he came third.
Cairns missed out on the K1 500 metre final after coming eighth in her semifinal Sunday.
She also ended up placed ninth in the K1 200 metre B final, and competed with sister Bridget Cairns in the C2 (two person canoe) 500 metre event.