I saw the following 34 aircraft at Cancun (CUN) on Monday, April 12, 2021:
4X-EDM 787-9 Dreamliner El Al Israel Airlines
9H-FAB ERJ-190-Lineage 1000 (ERJ-190-100 ECJ) Air X Charter
N266WN 737-7H4(WL) Southwest Airlines
N28457 737-924(ER)(WL) United Airlines
N334DN A321-211(WL) Delta Air Lines
N335DN A321-211(WL) Delta Air Lines
N339DN A321-211(WL) Delta Air Lines
N340DN A321-211(WL) Delta Air Lines
N461AS 737-990(ER)(WL) Alaska Airlines
N503VL A319-132 Volaris Costa Rica
N53441 737-924(ER)(WL) United Airlines
N62892 737-924(ER)(WL) United Airlines
N670NK A321-231(WL) Spirit Airlines
N690NK A320-232(WL) Spirit Airlines
N7728D 737-7BD(WL) Southwest Airlines
N7741C 737-7BD(WL) Southwest Airlines
N817AN 787-8 Dreamliner American Airlines
N817SY 737-8K2 Sun Country Airlines
N943JT A321-231(WL) JetBlue Airways
N979UY A321-231 American Airlines
TC-LLI 787-9 Dreamliner Turkish Airlines
XA-ADL 787-9 Dreamliner Aeromexico
XA-AEF ERJ-190-AR (ERJ-190-100 IGW) Aeromexico Connect
XA-MCE CRJ-200-ER (PF) MCS AeroCarga
XA-UCG 737-201 AVIACSA
XA-UZI MD-83 Aeronaves TSM
XA-VAE A320-232(WL) Viva Aerobus
XA-VDM 737-3H4(WL) Magnicharters
XA-VIK A320-271N(WL) Viva Aerobus
XA-VLB A320-233(WL) Volaris
XA-VLE A320-233(WL) Volaris
XA-VLY A321-231(WL) Volaris
XA-VOD A319-133 Volaris
XA-VRA A320-233(WL) Volaris