There were never any serious discussions about it for a number of reasons. First, all three nations you mention were not hostile to the US at the time of the formation of the Warsaw Pact and NATO. Expansion after formation of both organizations was rare and generally required special circumstance. NATO added Greece and Turkey in 1952 which sparked angry protests from the USSR but the Soviets were still in a position of relative weakness and couldn't do much about it. The admission of West Germany to NATO in 1955 is part of how the Soviets justified creating the Warsaw Pact and rearming East Germany. Neither organization expanded again until Spain joined NATO in 1982, as adding countries would be a good way to ratchet up tensions.

Although Cuba never joined the Warsaw Pact it did enjoy the benefits of Soviet protection, as part of the settlement of the Cuban Missile Crisis was a US pledge to not invade the island. However, actually incorporating it or Latin/Central American countries into the formal architecture would be a provocation that the US would almost certainly answer violently and represent an impossible challenge for the Soviets to supply and support the countries in the event of war. The Soviet Union was never good at projecting power beyond the Warsaw Pact and did not attempt another major overseas operation following the Cuban Missile Crisis until its support of Angola and Somalia in the 1970s. Neither operation went well and its likely that any attempt to significantly buttress Latin and Central American countries would fail significantly hurting Soviet prestige and undermine the basis of the Warsaw Pact itself.

It's also important to note that both were regional organizations. Turkey can count as a European country for these purposes in particular for its control of the Dardanelles which would limit the Soviet Black Sea Fleet. The U.S. was obviously included as it provided the protection and resources that the European powers sought in seeking the formation of NATO. Canada was included as well due to its relationship with Britain and the need for its help in keeping Atlantic sea routes clear. U.S. allies such as Australia and Japan were never considered for membership as they had no significant European interests, though they did fall into other treaty organizations such as SEATO. Thus including the countries you list would not serve the purpose of the Warsaw Pact as an Eastern Europe centered answer to NATO.