The character Jamie says 'today is a good day to die'. In the original, Kevin Bacon says 'hokahay' which is a Native American word which means today is a good day to die.
This movie is NOT a sequel to the 1990 movie. It is a remake, a re-imagining, or a version of the previous movie and has no other connection to it at all. Although Kiefer Sutherland appears in both versions, he plays two different characters.
Though they play classmates, Kiersey Clemons and Diego Luna are 14 years apart. Ray mentions being a firefighter prior to school, so it is possible he is an older student. Clemons is 8 years younger than James Norton, whose character is her peer.
The lunchroom where Courtney invites Jamie to meet her in the sub basement is located in Burwash Dining hall which is the second oldest of the residence buildings at Toronto's Victoria College. It's located at 73 Queen's Park Crescent. Many famous alum have eaten there including the father of Kiefer Sutherland, Donald who attended University of Toronto. Kiefer appeared in both Flatliner movies in 1990 and 2017.
The music box style music heard on the boat's radio at 1 hour 17 is exactly the same as was used in the horror film Banshee Chapter (2013). In Banshee Chapter it is explained as being commonly used by shortwave "number stations".